rfc4898.txt

Network Working Group                                          M. Mathis
Request for Comments: 4898                                    J. Heffner
Category: Standards Track               Pittsburgh Supercomputing Center
                                                         R. Raghunarayan
                                                           Cisco Systems
                                                                May 2007


                      TCP Extended Statistics MIB

Status of This Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The IETF Trust (2007).

Abstract

   This document describes extended performance statistics for TCP.
   They are designed to use TCP's ideal vantage point to diagnose
   performance problems in both the network and the application.  If a
   network-based application is performing poorly, TCP can determine if
   the bottleneck is in the sender, the receiver, or the network itself.
   If the bottleneck is in the network, TCP can provide specific
   information about its nature.

Table of Contents

   1. Introduction ....................................................2
   2. The Internet-Standard Management Framework ......................2
   3. Overview ........................................................2
      3.1. MIB Initialization and Persistence .........................4
      3.2. Relationship to TCP Standards ..............................4
      3.3. Diagnosing SYN-Flood Denial-of-Service Attacks .............6
   4. TCP Extended Statistics MIB .....................................7
   5. Security Considerations ........................................69
   6. IANA Considerations ............................................70
   7. Normative References ...........................................70
   8. Informative References .........................................72
   9. Contributors ...................................................73
   10. Acknowledgments ...............................................73




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1.  Introduction

   This document describes extended performance statistics for TCP.
   They are designed to use TCP's ideal vantage point to diagnose
   performance problems in both the network and the application.  If a
   network-based application is performing poorly, TCP can determine if
   the bottleneck is in the sender, the receiver, or the network itself.
   If the bottleneck is in the network, TCP can provide specific
   information about its nature.

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED",  "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119.

   The Simple Network Management Protocol (SNMP) objects defined in this
   document extend TCP MIB, as specified in RFC 4022 [RFC4022].  In
   addition to several new scalars and other objects, it augments two
   tables and makes one clarification to RFC 4022.  Existing management
   stations for the TCP MIB are expected to be fully compatible with
   these clarifications.

2.  The Internet-Standard Management Framework

   For a detailed overview of the documents that describe the current
   Internet-Standard Management Framework, please refer to section 7 of
   RFC 3410 [RFC3410].

   Managed objects are accessed via a virtual information store, termed
   the Management Information Base or MIB.  MIB objects are generally
   accessed through the Simple Network Management Protocol (SNMP).
   Objects in the MIB are defined using the mechanisms defined in the
   Structure of Management Information (SMI).  This memo specifies a MIB
   module that is compliant to the SMIv2, which is described in STD 58,
   RFC 2578 [RFC2578], STD 58, RFC 2579 [RFC2579] and STD 58, RFC 2580
   [RFC2580].

3.  Overview

   The TCP-ESTATS-MIB defined in this memo consists of two groups of
   scalars, seven tables, and two notifications:

   *  The first group of scalars contain statistics of the TCP protocol
      engine not covered in RFC 4022.  This group consists of the single
      scalar tcpEStatsListenerTableLastChange, which provides management
      stations with an easier mechanism to validate their listener
      caches.





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   *  The second group of scalars consist of knobs to enable and disable
      information collection by the tables containing connection-related
      statistics/information.  For example, the tcpEStatsControlPath
      object controls the activation of the tcpEStatsPathTable.  The
      tcpEStatsConnTableLatency object determines how long connection
      table rows are retained after a TCP connection transitions into
      the closed state.

   *  The tcpEStatsListenerTable augments tcpListenerTable in TCP-MIB
      [RFC4022] to provide additional information on the active TCP
      listeners on a device.  It supports objects to monitor and
      diagnose SYN-flood denial-of-service attacks as described below.

   *  The tcpEStatsConnectIdTable augments the tcpConnectionTable in
      TCP-MIB [RFC4022] to provide a mapping between connection 4-tuples
      (which index tcpConnectionTable) and an integer connection index,
      tcpEStatsConnectIndex.  The connection index is used to index into
      the five remaining tables in this MIB module, and is designed to
      facilitate rapid polling of multiple objects associated with one
      TCP connection.

   *  The tcpEStatsPerfTable contains objects that are useful for
      measuring TCP performance and first check problem diagnosis.

   *  The tcpEStatsPathTable contains objects that can be used to infer
      detailed behavior of the Internet path, such as the extent that
      there are segment losses or reordering, etc.

   *  The tcpEStatsStackTable contains objects that are most useful for
      determining how well the TCP control algorithms are coping with
      this particular path.

   *  The tcpEStatsAppTable provides objects that are useful for
      determining if the application using TCP is limiting TCP
      performance.

   *  The tcpEStatsTuneTable provides per-connection controls that can
      be used to work around a number of common problems that plague TCP
      over some paths.

   *  The two notifications defined in this MIB module are
      tcpEStatsEstablishNotification, indicating that a new connection
      has been accepted (or established, see below), and
      tcpEStatsCloseNotification, indicating that an existing connection
      has recently closed.






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3.1.  MIB Initialization and Persistence

   The TCP protocol itself is specifically designed not to preserve any
   state whatsoever across system reboots, and enforces this by
   requiring randomized Initial Sequence numbers and ephemeral ports
   under any conditions where segments from old connections might
   corrupt new connections following a reboot.

   All of the objects in the MIB MUST have the same persistence
   properties as the underlying TCP implementation.  On a reboot, all
   zero-based counters MUST be cleared, all dynamically created table
   rows MUST be deleted, and all read-write objects MUST be restored to
   their default values.  It is assumed that all TCP implementation have
   some initialization code (if nothing else, to set IP addresses) that
   has the opportunity to adjust tcpEStatsConnTableLatency and other
   read-write scalars controlling the creation of the various tables,
   before establishing the first TCP connection.  Implementations MAY
   also choose to make these control scalars persist across reboots.

   The ZeroBasedCounter32 and ZeroBasedCounter64 objects in the listener
   and connection tables are initialized to zero when the table row is
   created.

   The tcpEStatsConnTableLatency object determines how long connection
   table rows are retained after a TCP connection transitions into the
   closed state, to permit reading final connection completion
   statistics.  In RFC 4022 (TCP-MIB), the discussion of
   tcpConnectionTable row latency (page 9) the words "soon after" are
   understood to mean after tcpEStatsConnTableLatency, such that all
   rows of all tables associated with one connection are retained at
   least tcpEStatsConnTableLatency after connection close.  This
   clarification to RFC 4022 only applies when TCP-ESTATS-MIB is
   implemented.  If TCP-ESTATS-MIB is not implemented, RFC 4022 permits
   an unspecified delay between connection close and row deletion.

3.2.  Relationship to TCP Standards

   There are more than 70 RFCs and other documents that specify various
   aspects of the Transmission Control Protocol (TCP) [RFC4614].  While
   most protocols are completely specified in one or two documents, this
   has not proven to be feasible for TCP.  TCP implements a reliable
   end-to-end data transport service over a very weakly constrained IP
   datagram service.  The essential problem that TCP has to solve is
   balancing the applications need for fast and reliable data transport
   against the need to make fair, efficient, and equitable use of
   network resources, with only sparse information about the state of
   the network or its capabilities.




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   TCP maintains this balance through the use of many estimators and
   heuristics that regulate various aspects of the protocol.  For
   example, RFC 2988 describes how to calculate the retransmission timer
   (RTO) from the average and variance of the network round-trip-time
   (RTT), as estimated from the round-trip time sampled on some data
   segments.  Although these algorithms are standardized, they are a
   compromise which is optimal for only common Internet environments.
   Other estimators might yield better results (higher performance or
   more efficient use of the network) in some environments, particularly
   under uncommon conditions.

   It is the consensus of the community that nearly all of the
   estimators and heuristics used in TCP might be improved through
   further research and development.  For this reason, nearly all TCP
   documents leave some latitude for future improvements, for example,
   by the use of "SHOULD" instead of "MUST" [RFC2119].  Even standard
   algorithms that are required because they critically effect fairness
   or the dynamic stability of Internet congestion control, include some
   latitude for evolution.  As a consequence, there is considerable
   diversity in the details of the TCP implementations actually in use
   today.

   The fact that the underlying algorithms are not uniform makes it
   difficult to tightly specify a MIB.  We could have chosen the point
   of view that the MIB should publish precisely defined metrics of the
   network path, even if they are different from the estimators in use
   by TCP.  This would make the MIB more useful as a measurement tool,
   but less useful for understanding how any specific TCP implementation
   is interacting with the network path and upper protocol layers.  We
   chose instead to have the MIB expose the estimators and important
   states variables of the algorithms in use, without constraining the
   TCP implementation.

   As a consequence, the MIB objects are defined in terms of fairly
   abstract descriptions (e.g., round-trip time), but are intended to
   expose the actual estimators or other state variables as they are
   used in TCP implementations, possibly transformed (e.g., scaled or
   otherwise adjusted) to match the spirit of the object descriptions in
   this document.

   This may mean that MIB objects may not be exactly comparable between
   two different TCP implementations.  A general management station can
   only assume the abstract descriptions, which are useful for a general
   assessment of how TCP is functioning.  To a TCP implementer with
   detailed knowledge about the TCP implementation on a specific host,
   this MIB might be useful for debugging or evaluating the algorithms
   in their implementation.




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   Under no conditions is this MIB intended to constrain TCP to use (or
   exclude) any particular estimator, heuristic, algorithm, or
   implementation.

3.3.  Diagnosing SYN-Flood Denial-of-Service Attacks

   The tcpEStatsListenerTable is specifically designed to provide
   information that is useful for diagnosing SYN-flood Denial-of-Service
   attacks, where a server is overwhelmed by forged or otherwise
   malicious connection attempts.  There are several different
   techniques that can be used to defend against SYN-flooding but none
   are standardized [Edd06].  These different techniques all have the
   same basic characteristics that are instrumentable with a common set
   of objects, even though the techniques differ greatly in the details.

   All SYN-flood defenses avoid allocating significant resources (memory
   or CPU) to incoming (passive open) connections until the connections
   meet some liveness criteria (to defend against forged IP source
   addresses) and the server has sufficient resources to process the
   incoming request.  Note that allocating resources is an
   implementation-specific event that may not correspond to an
   observable protocol event (e.g., segments on the wire).  There are
   two general concepts that can be applied to all known SYN-flood
   defenses.  There is generally a well-defined event when a connection
   is allocated full resources, and a "backlog" -- a queue of embryonic
   connections that have been allocated only partial resources.

   In many implementations, incoming TCP connections are allocated
   resources as a side effect of the POSIX [POSIX] accept() call.  For
   this reason we use the terminology "accepting a connection" to refer
   to this event: committing sufficient network resources to process the
   incoming request.  Accepting a connection typically entails
   allocating memory for the protocol control block [RFC793], the per-
   connection table rows described in this MIB and CPU resources, such
   as process table entries or threads.

   Note that it is not useful to accept connections before they are
   ESTABLISHED, because this would create an easy opportunity for
   Denial-of-Service attacks, using forged source IP addresses.

   The backlog consists of connections that are in SYN-RCVD or
   ESTABLISHED states, that have not been accepted.  For purposes of
   this MIB, we assume that these connections have been allocated some
   resources (e.g., an embryonic protocol control block), but not full
   resources (e.g., do not yet have MIB table rows).






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   Note that some SYN-Flood defenses dispense with explicit SYN-RCVD
   state by cryptographically encoding the state in the ISS (initial
   sequence number sent) of the SYN-ACK (sometimes called a syn-cookie),
   and then using the sequence number of the first ACK to reconstruct
   the SYN-RCVD state before transitioning to the ESTABLISHED state.
   For these implementations there is no explicit representation of the
   SYN-RCVD state, and the backlog only consists of connections that are
   ESTABLISHED and are waiting to be ACCEPTED.

   Furthermore, most SYN-flood defenses have some mechanism to throttle
   connections that might otherwise overwhelm this endpoint.  They
   generally use some combination of discarding incoming SYNs and
   discarding connections already in the backlog.  This does not cause
   all connections from legitimate clients to fail, as long as the
   clients retransmit the SYN or first ACK as specified in RFC 793.
   Most diversity in SYN flood defenses arise from variations in these
   algorithms to limit load, and therefore cannot be instrumented with a
   common standard MIB.

   The Listen Table instruments all passively opened TCP connections in
   terms of observable protocol events (e.g., sent and received
   segments) and resource allocation events (entering the backlog and
   being accepted).  This approach eases generalization to SYN-flood
   mechanisms that use alternate TCP state transition diagrams and
   implicit mechanisms to encode some states.

4.  TCP Extended Statistics MIB

   This MIB module IMPORTS definitions from [RFC2578], [RFC2579],
   [RFC2580], [RFC2856], [RFC4022], and [RFC4502].  It uses REFERENCE
   clauses to refer to [RFC791], [RFC793], [RFC1122], [RFC1191],
   [RFC1323], [RFC2018], [RFC2581], [RFC2861], [RFC2883], [RFC2988],
   [RFC3168], [RFC3260], [RFC3517], [RFC3522], and [RFC3742].

   TCP-ESTATS-MIB DEFINITIONS ::= BEGIN
   IMPORTS
          MODULE-IDENTITY, Counter32, Integer32, Unsigned32,
          Gauge32, OBJECT-TYPE, mib-2,
          NOTIFICATION-TYPE
              FROM SNMPv2-SMI                 -- [RFC2578]
          MODULE-COMPLIANCE, OBJECT-GROUP, NOTIFICATION-GROUP
              FROM SNMPv2-CONF                -- [RFC2580]
          ZeroBasedCounter32
              FROM RMON2-MIB                  -- [RFC4502]
          ZeroBasedCounter64
              FROM HCNUM-TC                   -- [RFC2856]
          TEXTUAL-CONVENTION,
          DateAndTime, TruthValue, TimeStamp



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              FROM SNMPv2-TC                  -- [RFC2579]
          tcpListenerEntry, tcpConnectionEntry
              FROM TCP-MIB;                   -- [RFC4022]

   tcpEStatsMIB MODULE-IDENTITY
       LAST-UPDATED "200705180000Z"    -- 18 May 2007
       ORGANIZATION "IETF TSV Working Group"
       CONTACT-INFO
           "Matt Mathis
           John Heffner
           Web100 Project
           Pittsburgh Supercomputing Center
           300 S. Craig St.
           Pittsburgh, PA 15213
           Email: mathis@psc.edu, jheffner@psc.edu

           Rajiv Raghunarayan
           Cisco Systems Inc.
           San Jose, CA 95134
           Phone: 408 853 9612
           Email: raraghun@cisco.com

           Jon Saperia
           84 Kettell Plain Road
           Stow, MA 01775
           Phone: 617-201-2655
           Email: saperia@jdscons.com "
       DESCRIPTION
           "Documentation of TCP Extended Performance Instrumentation
            variables from the Web100 project.  [Web100]

            All of the objects in this MIB MUST have the same
            persistence properties as the underlying TCP implementation.
            On a reboot, all zero-based counters MUST be cleared, all
            dynamically created table rows MUST be deleted, and all
            read-write objects MUST be restored to their default values.

            It is assumed that all TCP implementation have some
            initialization code (if nothing else to set IP addresses)
            that has the opportunity to adjust tcpEStatsConnTableLatency
            and other read-write scalars controlling the creation of the
            various tables, before establishing the first TCP
            connection.  Implementations MAY also choose to make these
            control scalars persist across reboots.

            Copyright (C) The IETF Trust (2007).  This version
            of this MIB module is a part of RFC 4898; see the RFC
            itself for full legal notices."



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       REVISION "200705180000Z"    -- 18 May 2007
       DESCRIPTION
           "Initial version, published as RFC 4898."
           ::= { mib-2 156 }

   tcpEStatsNotifications OBJECT IDENTIFIER ::= { tcpEStatsMIB 0 }
   tcpEStatsMIBObjects    OBJECT IDENTIFIER ::= { tcpEStatsMIB 1 }
   tcpEStatsConformance   OBJECT IDENTIFIER ::= { tcpEStatsMIB 2 }
   tcpEStats             OBJECT IDENTIFIER ::= { tcpEStatsMIBObjects 1 }
   tcpEStatsControl      OBJECT IDENTIFIER ::= { tcpEStatsMIBObjects 2 }
   tcpEStatsScalar       OBJECT IDENTIFIER ::= { tcpEStatsMIBObjects 3 }

   --
   -- Textual Conventions
   --

   TcpEStatsNegotiated  ::= TEXTUAL-CONVENTION
      STATUS             current
      DESCRIPTION
          "Indicates if some optional TCP feature was negotiated.

           Enabled(1) indicates that the feature was successfully
           negotiated on, which generally requires both hosts to agree
           to use the feature.

           selfDisabled(2) indicates that the local host refused the
           feature because it is not implemented, configured off, or
           refused for some other reason, such as the lack of
           resources.

           peerDisabled(3) indicates that the local host was willing
           to negotiate the feature, but the remote host did not
           do so."
      SYNTAX INTEGER {
                   enabled(1),
                   selfDisabled(2),
                   peerDisabled(3)
           }

   --
   -- TCP Extended statistics scalars
   --

   tcpEStatsListenerTableLastChange OBJECT-TYPE
       SYNTAX     TimeStamp
       MAX-ACCESS read-only
       STATUS     current
       DESCRIPTION



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              "The value of sysUpTime at the time of the last
               creation or deletion of an entry in the tcpListenerTable.
               If the number of entries has been unchanged since the
               last re-initialization of the local network management
               subsystem, then this object contains a zero value."
       ::= { tcpEStatsScalar 3 }

   -- ================================================================
   --
   -- The tcpEStatsControl Group
   --

   -- The scalar objects in this group are used to control the
   -- activation and deactivation of the TCP Extended Statistics
   -- tables and notifications in this module.
   --

   tcpEStatsControlPath  OBJECT-TYPE
       SYNTAX          TruthValue
       MAX-ACCESS      read-write
       STATUS          current
       DESCRIPTION
           "Controls the activation of the TCP Path Statistics
           table.

           A value 'true' indicates that the TCP Path Statistics
           table is active, while 'false' indicates that the
           table is inactive."
       DEFVAL          { false }
       ::= { tcpEStatsControl 1 }

   tcpEStatsControlStack  OBJECT-TYPE
       SYNTAX          TruthValue
       MAX-ACCESS      read-write
       STATUS          current
       DESCRIPTION
           "Controls the activation of the TCP Stack Statistics
           table.

           A value 'true' indicates that the TCP Stack Statistics
           table is active, while 'false' indicates that the
           table is inactive."
       DEFVAL          { false }
       ::= { tcpEStatsControl 2 }

   tcpEStatsControlApp  OBJECT-TYPE
       SYNTAX          TruthValue
       MAX-ACCESS      read-write



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       STATUS          current
       DESCRIPTION
           "Controls the activation of the TCP Application
           Statistics table.

           A value 'true' indicates that the TCP Application
           Statistics table is active, while 'false' indicates
           that the table is inactive."
       DEFVAL          { false }
       ::= { tcpEStatsControl 3 }

   tcpEStatsControlTune  OBJECT-TYPE
       SYNTAX          TruthValue
       MAX-ACCESS      read-write
       STATUS          current
       DESCRIPTION
           "Controls the activation of the TCP Tuning table.

           A value 'true' indicates that the TCP Tuning
           table is active, while 'false' indicates that the
           table is inactive."
       DEFVAL          { false }
       ::= { tcpEStatsControl 4 }

   tcpEStatsControlNotify  OBJECT-TYPE
       SYNTAX          TruthValue
       MAX-ACCESS      read-write
       STATUS          current
       DESCRIPTION
           "Controls the generation of all notifications defined in
           this MIB.

           A value 'true' indicates that the notifications
           are active, while 'false' indicates that the
           notifications are inactive."
       DEFVAL          { false }
       ::= { tcpEStatsControl 5 }

   tcpEStatsConnTableLatency OBJECT-TYPE
       SYNTAX          Unsigned32
       UNITS           "seconds"
       MAX-ACCESS      read-write
       STATUS          current
       DESCRIPTION
           "Specifies the number of seconds that the entity will
            retain entries in the TCP connection tables, after the
            connection first enters the closed state.  The entity
            SHOULD provide a configuration option to enable



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            customization of this value.  A value of 0
            results in entries being removed from the tables as soon as
            the connection enters the closed state.  The value of
            this object pertains to the following tables:
              tcpEStatsConnectIdTable
              tcpEStatsPerfTable
              tcpEStatsPathTable
              tcpEStatsStackTable
              tcpEStatsAppTable
              tcpEStatsTuneTable"
       DEFVAL { 0 }
       ::= { tcpEStatsControl 6 }

   -- ================================================================
   --
   -- Listener Table
   --

   tcpEStatsListenerTable OBJECT-TYPE
       SYNTAX      SEQUENCE OF TcpEStatsListenerEntry
       MAX-ACCESS  not-accessible
       STATUS      current
       DESCRIPTION
           "This table contains information about TCP Listeners,
           in addition to the information maintained by the
           tcpListenerTable RFC 4022."
       ::= { tcpEStats 1 }

   tcpEStatsListenerEntry OBJECT-TYPE
       SYNTAX       TcpEStatsListenerEntry
       MAX-ACCESS   not-accessible
       STATUS       current
       DESCRIPTION
           "Each entry in the table contains information about
           a specific TCP Listener."
       AUGMENTS { tcpListenerEntry }
       ::= { tcpEStatsListenerTable 1 }

   TcpEStatsListenerEntry ::= SEQUENCE {
           tcpEStatsListenerStartTime         TimeStamp,
           tcpEStatsListenerSynRcvd           ZeroBasedCounter32,
           tcpEStatsListenerInitial           ZeroBasedCounter32,
           tcpEStatsListenerEstablished       ZeroBasedCounter32,
           tcpEStatsListenerAccepted          ZeroBasedCounter32,
           tcpEStatsListenerExceedBacklog     ZeroBasedCounter32,
           tcpEStatsListenerHCSynRcvd         ZeroBasedCounter64,
           tcpEStatsListenerHCInitial         ZeroBasedCounter64,
           tcpEStatsListenerHCEstablished     ZeroBasedCounter64,



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           tcpEStatsListenerHCAccepted        ZeroBasedCounter64,
           tcpEStatsListenerHCExceedBacklog   ZeroBasedCounter64,
           tcpEStatsListenerCurConns          Gauge32,
           tcpEStatsListenerMaxBacklog        Unsigned32,
           tcpEStatsListenerCurBacklog        Gauge32,
           tcpEStatsListenerCurEstabBacklog   Gauge32
   }

   tcpEStatsListenerStartTime   OBJECT-TYPE
       SYNTAX     TimeStamp
       MAX-ACCESS read-only
       STATUS     current
       DESCRIPTION
           "The value of sysUpTime at the time this listener was
           established.  If the current state was entered prior to
           the last re-initialization of the local network management
           subsystem, then this object contains a zero value."
       ::= { tcpEStatsListenerEntry 1 }

   tcpEStatsListenerSynRcvd OBJECT-TYPE
       SYNTAX     ZeroBasedCounter32
       MAX-ACCESS read-only
       STATUS     current
       DESCRIPTION
           "The number of SYNs which have been received for this
           listener.  The total number of failed connections for
           all reasons can be estimated to be tcpEStatsListenerSynRcvd
           minus tcpEStatsListenerAccepted and
           tcpEStatsListenerCurBacklog."
       ::= { tcpEStatsListenerEntry 2 }

   tcpEStatsListenerInitial     OBJECT-TYPE
      SYNTAX     ZeroBasedCounter32
      MAX-ACCESS read-only
      STATUS     current
      DESCRIPTION
         "The total number of connections for which the Listener
          has allocated initial state and placed the
          connection in the backlog.  This may happen in the
          SYN-RCVD or ESTABLISHED states, depending on the
          implementation."
       ::= { tcpEStatsListenerEntry 3 }

   tcpEStatsListenerEstablished OBJECT-TYPE
       SYNTAX     ZeroBasedCounter32
       MAX-ACCESS read-only
       STATUS     current
       DESCRIPTION



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           "The number of connections that have been established to
           this endpoint (e.g., the number of first ACKs that have
           been received for this listener)."
       ::= { tcpEStatsListenerEntry 4 }

   tcpEStatsListenerAccepted    OBJECT-TYPE
      SYNTAX     ZeroBasedCounter32
      MAX-ACCESS read-only
      STATUS     current
      DESCRIPTION
         "The total number of connections for which the Listener
          has successfully issued an accept, removing the connection
          from the backlog."
       ::= { tcpEStatsListenerEntry 5 }

   tcpEStatsListenerExceedBacklog OBJECT-TYPE
      SYNTAX     ZeroBasedCounter32
      MAX-ACCESS read-only
      STATUS     current
      DESCRIPTION
         "The total number of connections dropped from the
         backlog by this listener due to all reasons.  This
         includes all connections that are allocated initial
         resources, but are not accepted for some reason."
       ::= { tcpEStatsListenerEntry 6 }

   tcpEStatsListenerHCSynRcvd OBJECT-TYPE
       SYNTAX     ZeroBasedCounter64
       MAX-ACCESS read-only
       STATUS     current
       DESCRIPTION
           "The number of SYNs that have been received for this
           listener on systems that can process (or reject) more
           than 1 million connections per second.  See
           tcpEStatsListenerSynRcvd."
       ::= { tcpEStatsListenerEntry 7 }

   tcpEStatsListenerHCInitial     OBJECT-TYPE
      SYNTAX     ZeroBasedCounter64
      MAX-ACCESS read-only
      STATUS     current
      DESCRIPTION
         "The total number of connections for which the Listener
          has allocated initial state and placed the connection
          in the backlog on systems that can process (or reject)
          more than 1 million connections per second.  See
          tcpEStatsListenerInitial."
       ::= { tcpEStatsListenerEntry 8 }



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   tcpEStatsListenerHCEstablished OBJECT-TYPE
       SYNTAX     ZeroBasedCounter64
       MAX-ACCESS read-only
       STATUS     current
       DESCRIPTION
           "The number of connections that have been established to
           this endpoint on systems that can process (or reject) more
           than 1 million connections per second.  See
           tcpEStatsListenerEstablished."
       ::= { tcpEStatsListenerEntry 9 }

   tcpEStatsListenerHCAccepted    OBJECT-TYPE
      SYNTAX     ZeroBasedCounter64
      MAX-ACCESS read-only
      STATUS     current
      DESCRIPTION
         "The total number of connections for which the Listener
          has successfully issued an accept, removing the connection
          from the backlog on systems that can process (or reject)
          more than 1 million connections per second.  See
          tcpEStatsListenerAccepted."
       ::= { tcpEStatsListenerEntry 10 }

   tcpEStatsListenerHCExceedBacklog OBJECT-TYPE
      SYNTAX     ZeroBasedCounter64
      MAX-ACCESS read-only
      STATUS     current
      DESCRIPTION
         "The total number of connections dropped from the
         backlog by this listener due to all reasons on
         systems that can process (or reject) more than
         1 million connections per second.  See
         tcpEStatsListenerExceedBacklog."
       ::= { tcpEStatsListenerEntry 11 }

   tcpEStatsListenerCurConns   OBJECT-TYPE
      SYNTAX     Gauge32
      MAX-ACCESS read-only
      STATUS     current
      DESCRIPTION
         "The current number of connections in the ESTABLISHED
          state, which have also been accepted.  It excludes
          connections that have been established but not accepted
          because they are still subject to being discarded to
          shed load without explicit action by either endpoint."
       ::= { tcpEStatsListenerEntry 12 }

   tcpEStatsListenerMaxBacklog OBJECT-TYPE



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      SYNTAX     Unsigned32
      MAX-ACCESS read-only
      STATUS     current
      DESCRIPTION
         "The maximum number of connections allowed in the
          backlog at one time."
       ::= { tcpEStatsListenerEntry 13 }

   tcpEStatsListenerCurBacklog OBJECT-TYPE
      SYNTAX     Gauge32
      MAX-ACCESS read-only
      STATUS     current
      DESCRIPTION
         "The current number of connections that are in the backlog.
          This gauge includes connections in ESTABLISHED or
          SYN-RECEIVED states for which the Listener has not yet
          issued an accept.

          If this listener is using some technique to implicitly
          represent the SYN-RECEIVED states (e.g., by
          cryptographically encoding the state information in the
          initial sequence number, ISS), it MAY elect to exclude
          connections in the SYN-RECEIVED state from the backlog."
       ::= { tcpEStatsListenerEntry 14 }

   tcpEStatsListenerCurEstabBacklog OBJECT-TYPE
      SYNTAX     Gauge32
      MAX-ACCESS read-only
      STATUS     current
      DESCRIPTION
         "The current number of connections in the backlog that are
          in the ESTABLISHED state, but for which the Listener has
          not yet issued an accept."
       ::= { tcpEStatsListenerEntry 15 }


   -- ================================================================
   --
   -- TCP Connection ID Table
   --

   tcpEStatsConnectIdTable    OBJECT-TYPE
       SYNTAX      SEQUENCE OF TcpEStatsConnectIdEntry
       MAX-ACCESS  not-accessible
       STATUS      current
       DESCRIPTION
           "This table maps information that uniquely identifies
           each active TCP connection to the connection ID used by



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           other tables in this MIB Module.  It is an extension of
           tcpConnectionTable in RFC 4022.

           Entries are retained in this table for the number of
           seconds indicated by the tcpEStatsConnTableLatency
           object, after the TCP connection first enters the closed
           state."
       ::= { tcpEStats 2 }

   tcpEStatsConnectIdEntry  OBJECT-TYPE
       SYNTAX       TcpEStatsConnectIdEntry
       MAX-ACCESS   not-accessible
       STATUS       current
       DESCRIPTION
           "Each entry in this table maps a TCP connection
           4-tuple to a connection index."
       AUGMENTS { tcpConnectionEntry }
       ::= { tcpEStatsConnectIdTable 1 }

   TcpEStatsConnectIdEntry ::= SEQUENCE {
           tcpEStatsConnectIndex             Unsigned32
   }

   tcpEStatsConnectIndex  OBJECT-TYPE
       SYNTAX          Unsigned32 (1..4294967295)
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
           "A unique integer value assigned to each TCP Connection
           entry.

           The RECOMMENDED algorithm is to begin at 1 and increase to
           some implementation-specific maximum value and then start
           again at 1 skipping values already in use."
       ::= { tcpEStatsConnectIdEntry 1 }

   -- ================================================================
   --
   -- Basic TCP Performance Statistics
   --

   tcpEStatsPerfTable    OBJECT-TYPE
       SYNTAX      SEQUENCE OF TcpEStatsPerfEntry
       MAX-ACCESS  not-accessible
       STATUS      current
       DESCRIPTION

           "This table contains objects that are useful for



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           measuring TCP performance and first line problem
           diagnosis.  Most objects in this table directly expose
           some TCP state variable or are easily implemented as
           simple functions (e.g., the maximum value) of TCP
           state variables.

           Entries are retained in this table for the number of
           seconds indicated by the tcpEStatsConnTableLatency
           object, after the TCP connection first enters the closed
           state."
       ::= { tcpEStats 3 }

   tcpEStatsPerfEntry  OBJECT-TYPE
       SYNTAX       TcpEStatsPerfEntry
       MAX-ACCESS   not-accessible
       STATUS       current
       DESCRIPTION
           "Each entry in this table has information about the
           characteristics of each active and recently closed TCP
           connection."
      INDEX { tcpEStatsConnectIndex }
      ::= { tcpEStatsPerfTable 1 }

   TcpEStatsPerfEntry ::= SEQUENCE {

           tcpEStatsPerfSegsOut                ZeroBasedCounter32,
           tcpEStatsPerfDataSegsOut            ZeroBasedCounter32,
           tcpEStatsPerfDataOctetsOut          ZeroBasedCounter32,
           tcpEStatsPerfHCDataOctetsOut        ZeroBasedCounter64,
           tcpEStatsPerfSegsRetrans            ZeroBasedCounter32,
           tcpEStatsPerfOctetsRetrans          ZeroBasedCounter32,
           tcpEStatsPerfSegsIn                 ZeroBasedCounter32,
           tcpEStatsPerfDataSegsIn             ZeroBasedCounter32,
           tcpEStatsPerfDataOctetsIn           ZeroBasedCounter32,
           tcpEStatsPerfHCDataOctetsIn         ZeroBasedCounter64,
           tcpEStatsPerfElapsedSecs            ZeroBasedCounter32,
           tcpEStatsPerfElapsedMicroSecs       ZeroBasedCounter32,
           tcpEStatsPerfStartTimeStamp         DateAndTime,
           tcpEStatsPerfCurMSS                 Gauge32,
           tcpEStatsPerfPipeSize               Gauge32,
           tcpEStatsPerfMaxPipeSize            Gauge32,
           tcpEStatsPerfSmoothedRTT            Gauge32,
           tcpEStatsPerfCurRTO                 Gauge32,
           tcpEStatsPerfCongSignals            ZeroBasedCounter32,
           tcpEStatsPerfCurCwnd                Gauge32,
           tcpEStatsPerfCurSsthresh            Gauge32,
           tcpEStatsPerfTimeouts               ZeroBasedCounter32,
           tcpEStatsPerfCurRwinSent            Gauge32,



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           tcpEStatsPerfMaxRwinSent            Gauge32,
           tcpEStatsPerfZeroRwinSent           ZeroBasedCounter32,
           tcpEStatsPerfCurRwinRcvd            Gauge32,
           tcpEStatsPerfMaxRwinRcvd            Gauge32,
           tcpEStatsPerfZeroRwinRcvd           ZeroBasedCounter32,
           tcpEStatsPerfSndLimTransRwin        ZeroBasedCounter32,
           tcpEStatsPerfSndLimTransCwnd        ZeroBasedCounter32,
           tcpEStatsPerfSndLimTransSnd         ZeroBasedCounter32,
           tcpEStatsPerfSndLimTimeRwin         ZeroBasedCounter32,
           tcpEStatsPerfSndLimTimeCwnd         ZeroBasedCounter32,
           tcpEStatsPerfSndLimTimeSnd          ZeroBasedCounter32
       }

   --
   --  The following objects provide statistics on aggregate
   --  segments and data sent on a connection.  These provide a
   --  direct measure of the Internet capacity consumed by a
   --  connection.
   --

   tcpEStatsPerfSegsOut  OBJECT-TYPE
       SYNTAX          ZeroBasedCounter32
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "The total number of segments sent."
       ::= { tcpEStatsPerfEntry 1 }

   tcpEStatsPerfDataSegsOut  OBJECT-TYPE
       SYNTAX          ZeroBasedCounter32
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "The number of segments sent containing a positive length
           data segment."
       ::= { tcpEStatsPerfEntry 2 }

   tcpEStatsPerfDataOctetsOut  OBJECT-TYPE
       SYNTAX          ZeroBasedCounter32
       UNITS           "octets"
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "The number of octets of data contained in transmitted
           segments, including retransmitted data.  Note that this does
           not include TCP headers."
       ::= { tcpEStatsPerfEntry 3 }




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   tcpEStatsPerfHCDataOctetsOut  OBJECT-TYPE
       SYNTAX          ZeroBasedCounter64
       UNITS           "octets"
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "The number of octets of data contained in transmitted
           segments, including retransmitted data, on systems that can
           transmit more than 10 million bits per second.  Note that
           this does not include TCP headers."
       ::= { tcpEStatsPerfEntry 4 }

   tcpEStatsPerfSegsRetrans  OBJECT-TYPE
       SYNTAX          ZeroBasedCounter32
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "The number of segments transmitted containing at least some
           retransmitted data."
       REFERENCE
          "RFC 793, Transmission Control Protocol"
       ::= { tcpEStatsPerfEntry 5 }

   tcpEStatsPerfOctetsRetrans  OBJECT-TYPE
       SYNTAX          ZeroBasedCounter32
       UNITS           "octets"
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "The number of octets retransmitted."
       REFERENCE
          "RFC 793, Transmission Control Protocol"
       ::= { tcpEStatsPerfEntry 6 }

   tcpEStatsPerfSegsIn  OBJECT-TYPE
       SYNTAX          ZeroBasedCounter32
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "The total number of segments received."
       ::= { tcpEStatsPerfEntry 7 }

   tcpEStatsPerfDataSegsIn  OBJECT-TYPE
       SYNTAX          ZeroBasedCounter32
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "The number of segments received containing a positive



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           length data segment."
       ::= { tcpEStatsPerfEntry 8 }

   tcpEStatsPerfDataOctetsIn  OBJECT-TYPE
       SYNTAX          ZeroBasedCounter32
       UNITS           "octets"
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "The number of octets contained in received data segments,
           including retransmitted data.  Note that this does not
           include TCP headers."
       ::= { tcpEStatsPerfEntry 9 }

   tcpEStatsPerfHCDataOctetsIn  OBJECT-TYPE
       SYNTAX          ZeroBasedCounter64
       UNITS           "octets"
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "The number of octets contained in received data segments,
           including retransmitted data, on systems that can receive
           more than 10 million bits per second.  Note that this does
           not include TCP headers."
       ::= { tcpEStatsPerfEntry 10 }

   tcpEStatsPerfElapsedSecs  OBJECT-TYPE
       SYNTAX          ZeroBasedCounter32
       UNITS           "seconds"
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "The seconds part of the time elapsed between
           tcpEStatsPerfStartTimeStamp and the most recent protocol
           event (segment sent or received)."
       ::= { tcpEStatsPerfEntry 11 }

   tcpEStatsPerfElapsedMicroSecs  OBJECT-TYPE
       SYNTAX          ZeroBasedCounter32
       UNITS           "microseconds"
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "The micro-second part of time elapsed between
           tcpEStatsPerfStartTimeStamp to the most recent protocol
           event (segment sent or received).  This may be updated in
           whatever time granularity is the system supports."
       ::= { tcpEStatsPerfEntry 12 }



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   tcpEStatsPerfStartTimeStamp  OBJECT-TYPE
       SYNTAX          DateAndTime
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "Time at which this row was created and all
           ZeroBasedCounters in the row were initialized to zero."
       ::= { tcpEStatsPerfEntry 13 }

   --
   --  The following objects can be used to fit minimal
   --  performance models to the TCP data rate.
   --

   tcpEStatsPerfCurMSS  OBJECT-TYPE
       SYNTAX          Gauge32
       UNITS           "octets"
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "The current maximum segment size (MSS), in octets."
       REFERENCE
          "RFC 1122, Requirements for Internet Hosts - Communication
           Layers"
       ::= { tcpEStatsPerfEntry 14 }

   tcpEStatsPerfPipeSize  OBJECT-TYPE
       SYNTAX          Gauge32
       UNITS           "octets"
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "The TCP senders current estimate of the number of
           unacknowledged data octets in the network.

           While not in recovery (e.g., while the receiver is not
           reporting missing data to the sender), this is precisely the
           same as 'Flight size' as defined in RFC 2581, which can be
           computed as SND.NXT minus SND.UNA. [RFC793]

           During recovery, the TCP sender has incomplete information
           about the state of the network (e.g., which segments are
           lost vs reordered, especially if the return path is also
           dropping TCP acknowledgments).  Current TCP standards do not
           mandate any specific algorithm for estimating the number of
           unacknowledged data octets in the network.

           RFC 3517 describes a conservative algorithm to use SACK



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           information to estimate the number of unacknowledged data
           octets in the network. tcpEStatsPerfPipeSize object SHOULD
           be the same as 'pipe' as defined in RFC 3517 if it is
           implemented. (Note that while not in recovery the pipe
           algorithm yields the same values as flight size).

           If RFC 3517 is not implemented, the data octets in flight
           SHOULD be estimated as SND.NXT minus SND.UNA adjusted by
           some measure of the data that has left the network and
           retransmitted data.  For example, with Reno or NewReno style
           TCP, the number of duplicate acknowledgment is used to
           count the number of segments that have left the network.
           That is,
           PipeSize=SND.NXT-SND.UNA+(retransmits-dupacks)*CurMSS"
       REFERENCE
          "RFC 793, RFC 2581, RFC 3517"
       ::= { tcpEStatsPerfEntry 15 }

   tcpEStatsPerfMaxPipeSize  OBJECT-TYPE
       SYNTAX          Gauge32
       UNITS           "octets"
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "The maximum value of tcpEStatsPerfPipeSize, for this
           connection."
       REFERENCE
          "RFC 793, RFC 2581, RFC 3517"
       ::= { tcpEStatsPerfEntry 16 }

   tcpEStatsPerfSmoothedRTT  OBJECT-TYPE
       SYNTAX          Gauge32
       UNITS           "milliseconds"
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "The smoothed round trip time used in calculation of the
           RTO. See SRTT in [RFC2988]."
       REFERENCE
          "RFC 2988, Computing TCP's Retransmission Timer"
       ::= { tcpEStatsPerfEntry 17 }

   tcpEStatsPerfCurRTO  OBJECT-TYPE
       SYNTAX          Gauge32
       UNITS           "milliseconds"
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION



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          "The current value of the retransmit timer RTO."
       REFERENCE
          "RFC 2988, Computing TCP's Retransmission Timer"
       ::= { tcpEStatsPerfEntry 18 }

   tcpEStatsPerfCongSignals  OBJECT-TYPE
       SYNTAX          ZeroBasedCounter32
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "The number of multiplicative downward congestion window
           adjustments due to all forms of congestion signals,
           including Fast Retransmit, Explicit Congestion Notification
           (ECN), and timeouts.  This object summarizes all events that
           invoke the MD portion of Additive Increase Multiplicative
           Decrease (AIMD) congestion control, and as such is the best
           indicator of how a cwnd is being affected by congestion.

           Note that retransmission timeouts multiplicatively reduce
           the window implicitly by setting ssthresh, and SHOULD be
           included in tcpEStatsPerfCongSignals.  In order to minimize
           spurious congestion indications due to out-of-order
           segments, tcpEStatsPerfCongSignals SHOULD be incremented in
           association with the Fast Retransmit algorithm."
       REFERENCE
          "RFC 2581, TCP Congestion Control"
       ::= { tcpEStatsPerfEntry 19 }

   tcpEStatsPerfCurCwnd  OBJECT-TYPE
       SYNTAX          Gauge32
       UNITS           "octets"
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "The current congestion window, in octets."
       REFERENCE
          "RFC 2581, TCP Congestion Control"
       ::= { tcpEStatsPerfEntry 20 }

   tcpEStatsPerfCurSsthresh  OBJECT-TYPE
       SYNTAX          Gauge32
       UNITS           "octets"
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "The current slow start threshold in octets."
       REFERENCE
          "RFC 2581, TCP Congestion Control"



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       ::= { tcpEStatsPerfEntry 21 }

   tcpEStatsPerfTimeouts  OBJECT-TYPE
       SYNTAX          ZeroBasedCounter32
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "The number of times the retransmit timeout has expired when
           the RTO backoff multiplier is equal to one."
       REFERENCE
          "RFC 2988, Computing TCP's Retransmission Timer"
       ::= { tcpEStatsPerfEntry 22 }

   --
   --  The following objects instrument receiver window updates
   --  sent by the local receiver to the remote sender.  These can
   --  be used to determine if the local receiver is exerting flow
   --  control back pressure on the remote sender.
   --

   tcpEStatsPerfCurRwinSent  OBJECT-TYPE
       SYNTAX          Gauge32
       UNITS           "octets"
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "The most recent window advertisement sent, in octets."
       REFERENCE
          "RFC 793, Transmission Control Protocol"
       ::= { tcpEStatsPerfEntry 23 }

   tcpEStatsPerfMaxRwinSent  OBJECT-TYPE
       SYNTAX          Gauge32
       UNITS           "octets"
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "The maximum window advertisement sent, in octets."
       REFERENCE
          "RFC 793, Transmission Control Protocol"
       ::= { tcpEStatsPerfEntry 24 }

   tcpEStatsPerfZeroRwinSent  OBJECT-TYPE
       SYNTAX          ZeroBasedCounter32
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "The number of acknowledgments sent announcing a zero



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           receive window, when the previously announced window was
           not zero."
       REFERENCE
          "RFC 793, Transmission Control Protocol"
       ::= { tcpEStatsPerfEntry 25 }

   --
   --  The following objects instrument receiver window updates
   --  from the far end-system to determine if the remote receiver
   --  has sufficient buffer space or is exerting flow-control
   --  back pressure on the local sender.
   --

   tcpEStatsPerfCurRwinRcvd  OBJECT-TYPE
       SYNTAX          Gauge32
       UNITS           "octets"
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "The most recent window advertisement received, in octets."
       REFERENCE
          "RFC 793, Transmission Control Protocol"
       ::= { tcpEStatsPerfEntry 26 }

   tcpEStatsPerfMaxRwinRcvd  OBJECT-TYPE
       SYNTAX          Gauge32
       UNITS           "octets"
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "The maximum window advertisement received, in octets."
       REFERENCE
          "RFC 793, Transmission Control Protocol"
       ::= { tcpEStatsPerfEntry 27 }

   tcpEStatsPerfZeroRwinRcvd  OBJECT-TYPE
       SYNTAX          ZeroBasedCounter32
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "The number of acknowledgments received announcing a zero
           receive window, when the previously announced window was
           not zero."
       REFERENCE
          "RFC 793, Transmission Control Protocol"
       ::= { tcpEStatsPerfEntry 28 }

   --



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   --  The following optional objects can be used to quickly
   --  identify which subsystems are limiting TCP performance.
   --  There are three parallel pairs of instruments that measure
   --  the extent to which TCP performance is limited by the
   --  announced receiver window (indicating a receiver
   --  bottleneck), the current congestion window or
   --  retransmission timeout (indicating a path bottleneck) and
   --  all others events (indicating a sender bottleneck).
   --
   --  These instruments SHOULD be updated every time the TCP
   --  output routine stops sending data.  The elapsed time since
   --  the previous stop is accumulated into the appropriate
   --  object as determined by the previous stop reason (e.g.,
   --  stop state).  The current stop reason determines which timer
   --  will be updated the next time TCP output stops.
   --
   --  Since there is no explicit stop at the beginning of a
   --  timeout, it is necessary to retroactively reclassify the
   --  previous stop as 'Congestion Limited'.
   --

   tcpEStatsPerfSndLimTransRwin  OBJECT-TYPE
       SYNTAX          ZeroBasedCounter32
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "The number of transitions into the 'Receiver Limited' state
           from either the 'Congestion Limited' or 'Sender Limited'
           states.  This state is entered whenever TCP transmission
           stops because the sender has filled the announced receiver
           window, i.e., when SND.NXT has advanced to SND.UNA +
           SND.WND - 1 as described in RFC 793."
       REFERENCE
          "RFC 793, Transmission Control Protocol"
       ::= { tcpEStatsPerfEntry 31 }

   tcpEStatsPerfSndLimTransCwnd  OBJECT-TYPE
       SYNTAX          ZeroBasedCounter32
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "The number of transitions into the 'Congestion Limited'
           state from either the 'Receiver Limited' or 'Sender
           Limited' states.  This state is entered whenever TCP
           transmission stops because the sender has reached some
           limit defined by congestion control (e.g., cwnd) or other
           algorithms (retransmission timeouts) designed to control
           network traffic.  See the definition of 'CONGESTION WINDOW'



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           in RFC 2581."
       REFERENCE
          "RFC 2581, TCP Congestion Control"
       ::= { tcpEStatsPerfEntry 32 }

   tcpEStatsPerfSndLimTransSnd  OBJECT-TYPE
       SYNTAX          ZeroBasedCounter32
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "The number of transitions into the 'Sender Limited' state
           from either the 'Receiver Limited' or 'Congestion Limited'
           states.  This state is entered whenever TCP transmission
           stops due to some sender limit such as running out of
           application data or other resources and the Karn algorithm.
           When TCP stops sending data for any reason, which cannot be
           classified as Receiver Limited or Congestion Limited, it
           MUST be treated as Sender Limited."
       ::= { tcpEStatsPerfEntry 33 }

   tcpEStatsPerfSndLimTimeRwin  OBJECT-TYPE
       SYNTAX          ZeroBasedCounter32
       UNITS           "milliseconds"
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "The cumulative time spent in the 'Receiver Limited' state.
           See tcpEStatsPerfSndLimTransRwin."
       ::= { tcpEStatsPerfEntry 34 }

   tcpEStatsPerfSndLimTimeCwnd  OBJECT-TYPE
       SYNTAX          ZeroBasedCounter32
       UNITS           "milliseconds"
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "The cumulative time spent in the 'Congestion Limited'
           state.  See tcpEStatsPerfSndLimTransCwnd.  When there is a
           retransmission timeout, it SHOULD be counted in
           tcpEStatsPerfSndLimTimeCwnd (and not the cumulative time
           for some other state.)"
       ::= { tcpEStatsPerfEntry 35 }

   tcpEStatsPerfSndLimTimeSnd  OBJECT-TYPE
       SYNTAX          ZeroBasedCounter32
       UNITS           "milliseconds"
       MAX-ACCESS      read-only
       STATUS          current



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       DESCRIPTION
          "The cumulative time spent in the 'Sender Limited' state.
           See tcpEStatsPerfSndLimTransSnd."
       ::= { tcpEStatsPerfEntry 36 }

   -- ================================================================
   --
   -- Statistics for diagnosing path problems
   --

   tcpEStatsPathTable    OBJECT-TYPE
       SYNTAX      SEQUENCE OF TcpEStatsPathEntry
       MAX-ACCESS  not-accessible
       STATUS      current
       DESCRIPTION
           "This table contains objects that can be used to infer
           detailed behavior of the Internet path, such as the
           extent that there is reordering, ECN bits, and if
           RTT fluctuations are correlated to losses.

           Entries are retained in this table for the number of
           seconds indicated by the tcpEStatsConnTableLatency
           object, after the TCP connection first enters the closed
           state."
       ::= { tcpEStats 4 }

   tcpEStatsPathEntry  OBJECT-TYPE
       SYNTAX       TcpEStatsPathEntry
       MAX-ACCESS   not-accessible
       STATUS       current
       DESCRIPTION
           "Each entry in this table has information about the
           characteristics of each active and recently closed TCP
           connection."
      INDEX { tcpEStatsConnectIndex }
      ::= { tcpEStatsPathTable 1 }

   TcpEStatsPathEntry ::= SEQUENCE {

           tcpEStatsPathRetranThresh           Gauge32,
           tcpEStatsPathNonRecovDAEpisodes     ZeroBasedCounter32,
           tcpEStatsPathSumOctetsReordered     ZeroBasedCounter32,
           tcpEStatsPathNonRecovDA             ZeroBasedCounter32,
           tcpEStatsPathSampleRTT              Gauge32,
           tcpEStatsPathRTTVar                 Gauge32,
           tcpEStatsPathMaxRTT                 Gauge32,
           tcpEStatsPathMinRTT                 Gauge32,
           tcpEStatsPathSumRTT                 ZeroBasedCounter32,



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           tcpEStatsPathHCSumRTT               ZeroBasedCounter64,
           tcpEStatsPathCountRTT               ZeroBasedCounter32,
           tcpEStatsPathMaxRTO                 Gauge32,
           tcpEStatsPathMinRTO                 Gauge32,
           tcpEStatsPathIpTtl                  Unsigned32,
           tcpEStatsPathIpTosIn                OCTET STRING,
           tcpEStatsPathIpTosOut               OCTET STRING,
           tcpEStatsPathPreCongSumCwnd         ZeroBasedCounter32,
           tcpEStatsPathPreCongSumRTT          ZeroBasedCounter32,
           tcpEStatsPathPostCongSumRTT         ZeroBasedCounter32,
           tcpEStatsPathPostCongCountRTT       ZeroBasedCounter32,
           tcpEStatsPathECNsignals             ZeroBasedCounter32,
           tcpEStatsPathDupAckEpisodes         ZeroBasedCounter32,
           tcpEStatsPathRcvRTT                 Gauge32,
           tcpEStatsPathDupAcksOut             ZeroBasedCounter32,
           tcpEStatsPathCERcvd                 ZeroBasedCounter32,
           tcpEStatsPathECESent                ZeroBasedCounter32
       }

   --
   --  The following optional objects can be used to infer segment
   --  reordering on the path from the local sender to the remote
   --  receiver.
   --

   tcpEStatsPathRetranThresh  OBJECT-TYPE
       SYNTAX          Gauge32
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "The number of duplicate acknowledgments required to trigger
           Fast Retransmit.  Note that although this is constant in
           traditional Reno TCP implementations, it is adaptive in
           many newer TCPs."
       REFERENCE
          "RFC 2581, TCP Congestion Control"
       ::= { tcpEStatsPathEntry 1 }

   tcpEStatsPathNonRecovDAEpisodes  OBJECT-TYPE
       SYNTAX          ZeroBasedCounter32
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "The number of duplicate acknowledgment episodes that did
           not trigger a Fast Retransmit because ACK advanced prior to
           the number of duplicate acknowledgments reaching
           RetranThresh.




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           In many implementations this is the number of times the
           'dupacks' counter is set to zero when it is non-zero but
           less than RetranThresh.

           Note that the change in tcpEStatsPathNonRecovDAEpisodes
           divided by the change in tcpEStatsPerfDataSegsOut is an
           estimate of the frequency of data reordering on the forward
           path over some interval."
       REFERENCE
          "RFC 2581, TCP Congestion Control"
       ::= { tcpEStatsPathEntry 2 }

   tcpEStatsPathSumOctetsReordered  OBJECT-TYPE
       SYNTAX          ZeroBasedCounter32
       UNITS           "octets"
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "The sum of the amounts SND.UNA advances on the
           acknowledgment which ends a dup-ack episode without a
           retransmission.

           Note the change in tcpEStatsPathSumOctetsReordered divided
           by the change in tcpEStatsPathNonRecovDAEpisodes is an
           estimates of the average reordering distance, over some
           interval."
       ::= { tcpEStatsPathEntry 3 }

   tcpEStatsPathNonRecovDA  OBJECT-TYPE
       SYNTAX          ZeroBasedCounter32
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "Duplicate acks (or SACKS) that did not trigger a Fast
           Retransmit because ACK advanced prior to the number of
           duplicate acknowledgments reaching RetranThresh.

           In many implementations, this is the sum of the 'dupacks'
           counter, just before it is set to zero because ACK advanced
           without a Fast Retransmit.

           Note that the change in tcpEStatsPathNonRecovDA divided by
           the change in tcpEStatsPathNonRecovDAEpisodes is an
           estimate of the average reordering distance in segments
           over some interval."
       REFERENCE
          "RFC 2581, TCP Congestion Control"
       ::= { tcpEStatsPathEntry 4 }



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   --
   --  The following optional objects instrument the round trip
   --  time estimator and the retransmission timeout timer.
   --

   tcpEStatsPathSampleRTT  OBJECT-TYPE
       SYNTAX          Gauge32
       UNITS           "milliseconds"
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "The most recent raw round trip time measurement used in
           calculation of the RTO."
       REFERENCE
          "RFC 2988, Computing TCP's Retransmission Timer"
       ::= { tcpEStatsPathEntry 11 }

   tcpEStatsPathRTTVar  OBJECT-TYPE
       SYNTAX          Gauge32
       UNITS           "milliseconds"
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "The round trip time variation used in calculation of the
           RTO.  See RTTVAR in [RFC2988]."
       REFERENCE
          "RFC 2988, Computing TCP's Retransmission Timer"
       ::= { tcpEStatsPathEntry 12 }

   tcpEStatsPathMaxRTT  OBJECT-TYPE
       SYNTAX          Gauge32
       UNITS           "milliseconds"
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "The maximum sampled round trip time."
       REFERENCE
          "RFC 2988, Computing TCP's Retransmission Timer"
       ::= { tcpEStatsPathEntry 13 }

   tcpEStatsPathMinRTT  OBJECT-TYPE
       SYNTAX          Gauge32
       UNITS           "milliseconds"
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "The minimum sampled round trip time."
       REFERENCE



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          "RFC 2988, Computing TCP's Retransmission Timer"
       ::= { tcpEStatsPathEntry 14 }

   tcpEStatsPathSumRTT  OBJECT-TYPE
       SYNTAX          ZeroBasedCounter32
       UNITS           "milliseconds"
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "The sum of all sampled round trip times.

           Note that the change in tcpEStatsPathSumRTT divided by the
           change in tcpEStatsPathCountRTT is the mean RTT, uniformly
           averaged over an enter interval."
       REFERENCE
          "RFC 2988, Computing TCP's Retransmission Timer"
       ::= { tcpEStatsPathEntry 15 }

   tcpEStatsPathHCSumRTT  OBJECT-TYPE
       SYNTAX          ZeroBasedCounter64
       UNITS           "milliseconds"
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "The sum of all sampled round trip times, on all systems
           that implement multiple concurrent RTT measurements.

           Note that the change in tcpEStatsPathHCSumRTT divided by
           the change in tcpEStatsPathCountRTT is the mean RTT,
           uniformly averaged over an enter interval."
       REFERENCE
          "RFC 2988, Computing TCP's Retransmission Timer"
       ::= { tcpEStatsPathEntry 16 }

   tcpEStatsPathCountRTT  OBJECT-TYPE
       SYNTAX          ZeroBasedCounter32
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "The number of round trip time samples included in
           tcpEStatsPathSumRTT and tcpEStatsPathHCSumRTT."
       REFERENCE
          "RFC 2988, Computing TCP's Retransmission Timer"
       ::= { tcpEStatsPathEntry 17 }

   tcpEStatsPathMaxRTO  OBJECT-TYPE
       SYNTAX          Gauge32
       UNITS           "milliseconds"



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       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "The maximum value of the retransmit timer RTO."
       REFERENCE
          "RFC 2988, Computing TCP's Retransmission Timer"
       ::= { tcpEStatsPathEntry 18 }

   tcpEStatsPathMinRTO  OBJECT-TYPE
       SYNTAX          Gauge32
       UNITS           "milliseconds"
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "The minimum value of the retransmit timer RTO."
       REFERENCE
          "RFC 2988, Computing TCP's Retransmission Timer"
       ::= { tcpEStatsPathEntry 19 }

   --
   --  The following optional objects provide information about
   --  how TCP is using the IP layer.
   --

   tcpEStatsPathIpTtl  OBJECT-TYPE
       SYNTAX          Unsigned32
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "The value of the TTL field carried in the most recently
           received IP header.  This is sometimes useful to detect
           changing or unstable routes."
       REFERENCE
          "RFC 791, Internet Protocol"
       ::= { tcpEStatsPathEntry 20 }

   tcpEStatsPathIpTosIn  OBJECT-TYPE
       SYNTAX          OCTET STRING (SIZE(1))
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "The value of the IPv4 Type of Service octet, or the IPv6
           traffic class octet, carried in the most recently received
           IP header.

           This is useful to diagnose interactions between TCP and any
           IP layer packet scheduling and delivery policy, which might
           be in effect to implement Diffserv."



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       REFERENCE
          "RFC 3260, New Terminology and Clarifications for Diffserv"
       ::= { tcpEStatsPathEntry 21 }

   tcpEStatsPathIpTosOut  OBJECT-TYPE
       SYNTAX          OCTET STRING (SIZE(1))
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "The value of the IPv4 Type Of Service octet, or the IPv6
           traffic class octet, carried in the most recently
           transmitted IP header.

           This is useful to diagnose interactions between TCP and any
           IP layer packet scheduling and delivery policy, which might
           be in effect to implement Diffserv."
       REFERENCE
          "RFC 3260, New Terminology and Clarifications for Diffserv"
       ::= { tcpEStatsPathEntry 22 }

   --
   --  The following optional objects characterize the congestion
   --  feedback signals by collecting statistics on how the
   --  congestion events are correlated to losses, changes in RTT
   --  and other protocol events.
   --

   tcpEStatsPathPreCongSumCwnd  OBJECT-TYPE
       SYNTAX          ZeroBasedCounter32
       UNITS           "octets"
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "The sum of the values of the congestion window, in octets,
           captured each time a congestion signal is received.  This
           MUST be updated each time tcpEStatsPerfCongSignals is
           incremented, such that the change in
           tcpEStatsPathPreCongSumCwnd divided by the change in
           tcpEStatsPerfCongSignals is the average window (over some
           interval) just prior to a congestion signal."
       ::= { tcpEStatsPathEntry 23 }

   tcpEStatsPathPreCongSumRTT  OBJECT-TYPE
       SYNTAX          ZeroBasedCounter32
       UNITS           "milliseconds"
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION



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          "Sum of the last sample of the RTT (tcpEStatsPathSampleRTT)
           prior to the received congestion signals.  This MUST be
           updated each time tcpEStatsPerfCongSignals is incremented,
           such that the change in tcpEStatsPathPreCongSumRTT divided by
           the change in tcpEStatsPerfCongSignals is the average RTT
           (over some interval) just prior to a congestion signal."
       ::= { tcpEStatsPathEntry 24 }

   tcpEStatsPathPostCongSumRTT  OBJECT-TYPE
       SYNTAX          ZeroBasedCounter32
       UNITS           "octets"
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "Sum of the first sample of the RTT (tcpEStatsPathSampleRTT)
           following each congestion signal.  Such that the change in
           tcpEStatsPathPostCongSumRTT divided by the change in
           tcpEStatsPathPostCongCountRTT is the average RTT (over some
           interval) just after a congestion signal."
       ::= { tcpEStatsPathEntry 25 }

   tcpEStatsPathPostCongCountRTT  OBJECT-TYPE
       SYNTAX          ZeroBasedCounter32
       UNITS           "milliseconds"
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "The number of RTT samples included in
           tcpEStatsPathPostCongSumRTT such that the change in
           tcpEStatsPathPostCongSumRTT divided by the change in
           tcpEStatsPathPostCongCountRTT is the average RTT (over some
           interval) just after a congestion signal."
       ::= { tcpEStatsPathEntry 26 }

   --
   --  The following optional objects can be used to detect other
   --  types of non-loss congestion signals such as source quench
   --  or ECN.
   --

   tcpEStatsPathECNsignals  OBJECT-TYPE
       SYNTAX          ZeroBasedCounter32
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "The number of congestion signals delivered to the TCP
           sender via explicit congestion notification (ECN).  This is
           typically the number of segments bearing Echo Congestion



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           Experienced (ECE) bits, but
           should also include segments failing the ECN nonce check or
           other explicit congestion signals."
       REFERENCE
          "RFC 3168, The Addition of Explicit Congestion Notification
           (ECN) to IP"
       ::= { tcpEStatsPathEntry 27 }

   --
   --  The following optional objects are receiver side
   --  instruments of the path from the sender to the receiver.  In
   --  general, the receiver has less information about the state
   --  of the path because the receiver does not have a robust
   --  mechanism to infer the sender's actions.
   --

   tcpEStatsPathDupAckEpisodes  OBJECT-TYPE
       SYNTAX          ZeroBasedCounter32
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "The number of Duplicate Acks Sent when prior Ack was not
           duplicate.  This is the number of times that a contiguous
           series of duplicate acknowledgments have been sent.

           This is an indication of the number of data segments lost
           or reordered on the path from the remote TCP endpoint to
           the near TCP endpoint."
       REFERENCE
          "RFC 2581, TCP Congestion Control"
       ::= { tcpEStatsPathEntry 28 }

   tcpEStatsPathRcvRTT  OBJECT-TYPE
       SYNTAX          Gauge32
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "The receiver's estimate of the Path RTT.

           Adaptive receiver window algorithms depend on the receiver
           to having a good estimate of the path RTT."
       ::= { tcpEStatsPathEntry 29 }

   tcpEStatsPathDupAcksOut  OBJECT-TYPE
       SYNTAX          ZeroBasedCounter32
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION



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          "The number of duplicate ACKs sent.  The ratio of the change
           in tcpEStatsPathDupAcksOut to the change in
           tcpEStatsPathDupAckEpisodes is an indication of reorder or
           recovery distance over some interval."
       REFERENCE
          "RFC 2581, TCP Congestion Control"
       ::= { tcpEStatsPathEntry 30 }

   tcpEStatsPathCERcvd  OBJECT-TYPE
       SYNTAX          ZeroBasedCounter32
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "The number of segments received with IP headers bearing
           Congestion Experienced (CE) markings."
       REFERENCE
          "RFC 3168, The Addition of Explicit Congestion Notification
           (ECN) to IP"
       ::= { tcpEStatsPathEntry 31 }

   tcpEStatsPathECESent  OBJECT-TYPE
       SYNTAX          ZeroBasedCounter32
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "Number of times the Echo Congestion Experienced (ECE) bit
           in the TCP header has been set (transitioned from 0 to 1),
           due to a Congestion Experienced (CE) marking on an IP
           header.  Note that ECE can be set and reset only once per
           RTT, while CE can be set on many segments per RTT."
       REFERENCE
          "RFC 3168, The Addition of Explicit Congestion Notification
           (ECN) to IP"
       ::= { tcpEStatsPathEntry 32 }

   -- ================================================================
   --
   -- Statistics for diagnosing stack algorithms
   --

   tcpEStatsStackTable    OBJECT-TYPE
       SYNTAX      SEQUENCE OF TcpEStatsStackEntry
       MAX-ACCESS  not-accessible
       STATUS      current
       DESCRIPTION
           "This table contains objects that are most useful for
           determining how well some of the TCP control
           algorithms are coping with this particular



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           path.

           Entries are retained in this table for the number of
           seconds indicated by the tcpEStatsConnTableLatency
           object, after the TCP connection first enters the closed
           state."
       ::= { tcpEStats 5 }

   tcpEStatsStackEntry  OBJECT-TYPE
       SYNTAX       TcpEStatsStackEntry
       MAX-ACCESS   not-accessible
       STATUS       current
       DESCRIPTION
           "Each entry in this table has information about the
           characteristics of each active and recently closed TCP
           connection."
      INDEX { tcpEStatsConnectIndex }
      ::= { tcpEStatsStackTable 1 }

   TcpEStatsStackEntry ::= SEQUENCE {

           tcpEStatsStackActiveOpen            TruthValue,
           tcpEStatsStackMSSSent               Unsigned32,
           tcpEStatsStackMSSRcvd               Unsigned32,
           tcpEStatsStackWinScaleSent          Integer32,
           tcpEStatsStackWinScaleRcvd          Integer32,
           tcpEStatsStackTimeStamps            TcpEStatsNegotiated,
           tcpEStatsStackECN                   TcpEStatsNegotiated,
           tcpEStatsStackWillSendSACK          TcpEStatsNegotiated,
           tcpEStatsStackWillUseSACK           TcpEStatsNegotiated,
           tcpEStatsStackState                 INTEGER,
           tcpEStatsStackNagle                 TruthValue,
           tcpEStatsStackMaxSsCwnd             Gauge32,
           tcpEStatsStackMaxCaCwnd             Gauge32,
           tcpEStatsStackMaxSsthresh           Gauge32,
           tcpEStatsStackMinSsthresh           Gauge32,
           tcpEStatsStackInRecovery            INTEGER,
           tcpEStatsStackDupAcksIn             ZeroBasedCounter32,
           tcpEStatsStackSpuriousFrDetected    ZeroBasedCounter32,
           tcpEStatsStackSpuriousRtoDetected   ZeroBasedCounter32,
           tcpEStatsStackSoftErrors            ZeroBasedCounter32,
           tcpEStatsStackSoftErrorReason       INTEGER,
           tcpEStatsStackSlowStart             ZeroBasedCounter32,
           tcpEStatsStackCongAvoid             ZeroBasedCounter32,
           tcpEStatsStackOtherReductions       ZeroBasedCounter32,
           tcpEStatsStackCongOverCount         ZeroBasedCounter32,
           tcpEStatsStackFastRetran            ZeroBasedCounter32,
           tcpEStatsStackSubsequentTimeouts    ZeroBasedCounter32,



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           tcpEStatsStackCurTimeoutCount       Gauge32,
           tcpEStatsStackAbruptTimeouts        ZeroBasedCounter32,
           tcpEStatsStackSACKsRcvd             ZeroBasedCounter32,
           tcpEStatsStackSACKBlocksRcvd        ZeroBasedCounter32,
           tcpEStatsStackSendStall             ZeroBasedCounter32,
           tcpEStatsStackDSACKDups             ZeroBasedCounter32,
           tcpEStatsStackMaxMSS                Gauge32,
           tcpEStatsStackMinMSS                Gauge32,
           tcpEStatsStackSndInitial            Unsigned32,
           tcpEStatsStackRecInitial            Unsigned32,
           tcpEStatsStackCurRetxQueue          Gauge32,
           tcpEStatsStackMaxRetxQueue          Gauge32,
           tcpEStatsStackCurReasmQueue         Gauge32,
           tcpEStatsStackMaxReasmQueue         Gauge32
       }

   --
   --  The following objects reflect TCP options carried on the
   --  SYN or SYN-ACK.  These options are used to provide
   --  additional protocol parameters or to enable various
   --  optional TCP features or algorithms.
   --
   --  Except as noted, the TCP protocol does not permit these
   --  options to change after the SYN exchange.
   --

   tcpEStatsStackActiveOpen  OBJECT-TYPE
       SYNTAX          TruthValue
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "True(1) if the local connection traversed the SYN-SENT
           state, else false(2)."
       REFERENCE
          "RFC 793, Transmission Control Protocol"
       ::= { tcpEStatsStackEntry 1 }

   tcpEStatsStackMSSSent  OBJECT-TYPE
       SYNTAX          Unsigned32
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "The value sent in an MSS option, or zero if none."
       REFERENCE
          "RFC 1122, Requirements for Internet Hosts - Communication
           Layers"
       ::= { tcpEStatsStackEntry 2 }




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   tcpEStatsStackMSSRcvd  OBJECT-TYPE
       SYNTAX          Unsigned32
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "The value received in an MSS option, or zero if none."
       REFERENCE
          "RFC 1122, Requirements for Internet Hosts - Communication
           Layers"
       ::= { tcpEStatsStackEntry 3 }

   tcpEStatsStackWinScaleSent  OBJECT-TYPE
       SYNTAX          Integer32 (-1..14)
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "The value of the transmitted window scale option if one was
           sent; otherwise, a value of -1.

           Note that if both tcpEStatsStackWinScaleSent and
           tcpEStatsStackWinScaleRcvd are not -1, then Rcv.Wind.Scale
           will be the same as this value and used to scale receiver
           window announcements from the local host to the remote
           host."
       REFERENCE
          "RFC 1323, TCP Extensions for High Performance"
       ::= { tcpEStatsStackEntry 4 }

   tcpEStatsStackWinScaleRcvd  OBJECT-TYPE
       SYNTAX          Integer32 (-1..14)
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "The value of the received window scale option if one was
           received; otherwise, a value of -1.

           Note that if both tcpEStatsStackWinScaleSent and
           tcpEStatsStackWinScaleRcvd are not -1, then Snd.Wind.Scale
           will be the same as this value and used to scale receiver
           window announcements from the remote host to the local
           host."
       REFERENCE
          "RFC 1323, TCP Extensions for High Performance"
       ::= { tcpEStatsStackEntry 5 }

   tcpEStatsStackTimeStamps  OBJECT-TYPE
       SYNTAX          TcpEStatsNegotiated
       MAX-ACCESS      read-only



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       STATUS          current
       DESCRIPTION
          "Enabled(1) if TCP timestamps have been negotiated on,
           selfDisabled(2) if they are disabled or not implemented on
           the local host, or peerDisabled(3) if not negotiated by the
           remote hosts."
       REFERENCE
          "RFC 1323, TCP Extensions for High Performance"
       ::= { tcpEStatsStackEntry 6 }

   tcpEStatsStackECN  OBJECT-TYPE
       SYNTAX          TcpEStatsNegotiated
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "Enabled(1) if Explicit Congestion Notification (ECN) has
           been negotiated on, selfDisabled(2) if it is disabled or
           not implemented on the local host, or peerDisabled(3) if
           not negotiated by the remote hosts."
       REFERENCE
          "RFC 3168, The Addition of Explicit Congestion Notification
           (ECN) to IP"
       ::= { tcpEStatsStackEntry 7 }

   tcpEStatsStackWillSendSACK  OBJECT-TYPE
       SYNTAX          TcpEStatsNegotiated
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "Enabled(1) if the local host will send SACK options,
           selfDisabled(2) if SACK is disabled or not implemented on
           the local host, or peerDisabled(3) if the remote host did
           not send the SACK-permitted option.

           Note that SACK negotiation is not symmetrical.  SACK can
           enabled on one side of the connection and not the other."
       REFERENCE
          "RFC 2018, TCP Selective Acknowledgement Options"
       ::= { tcpEStatsStackEntry 8 }

   tcpEStatsStackWillUseSACK  OBJECT-TYPE
       SYNTAX          TcpEStatsNegotiated
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "Enabled(1) if the local host will process SACK options,
           selfDisabled(2) if SACK is disabled or not implemented on
           the local host, or peerDisabled(3) if the remote host sends



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           duplicate ACKs without SACK options, or the local host
           otherwise decides not to process received SACK options.

           Unlike other TCP options, the remote data receiver cannot
           explicitly indicate if it is able to generate SACK options.
           When sending data, the local host has to deduce if the
           remote receiver is sending SACK options.  This object can
           transition from Enabled(1) to peerDisabled(3) after the SYN
           exchange.

           Note that SACK negotiation is not symmetrical.  SACK can
           enabled on one side of the connection and not the other."
       REFERENCE
          "RFC 2018, TCP Selective Acknowledgement Options"
       ::= { tcpEStatsStackEntry 9 }

   --
   --  The following two objects reflect the current state of the
   --  connection.
   --

   tcpEStatsStackState  OBJECT-TYPE
       SYNTAX          INTEGER {
          tcpESStateClosed(1),
          tcpESStateListen(2),
          tcpESStateSynSent(3),
          tcpESStateSynReceived(4),
          tcpESStateEstablished(5),
          tcpESStateFinWait1(6),
          tcpESStateFinWait2(7),
          tcpESStateCloseWait(8),
          tcpESStateLastAck(9),
          tcpESStateClosing(10),
          tcpESStateTimeWait(11),
          tcpESStateDeleteTcb(12)
       }
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "An integer value representing the connection state from the
           TCP State Transition Diagram.

           The value listen(2) is included only for parallelism to the
           old tcpConnTable, and SHOULD NOT be used because the listen
           state in managed by the tcpListenerTable.

           The value DeleteTcb(12) is included only for parallelism to
           the tcpConnTable mechanism for terminating connections,



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           although this table does not permit writing."
       REFERENCE
          "RFC 793, Transmission Control Protocol"
       ::= { tcpEStatsStackEntry 10 }

   tcpEStatsStackNagle  OBJECT-TYPE
       SYNTAX          TruthValue
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "True(1) if the Nagle algorithm is being used, else
           false(2)."
       REFERENCE
          "RFC 1122, Requirements for Internet Hosts - Communication
           Layers"
       ::= { tcpEStatsStackEntry 11 }

   --
   --  The following objects instrument the overall operation of
   --  TCP congestion control and data retransmissions.  These
   --  instruments are sufficient to fit the actual performance to
   --  an updated macroscopic performance model [RFC2581] [Mat97]
   --  [Pad98].
   --

   tcpEStatsStackMaxSsCwnd  OBJECT-TYPE
       SYNTAX          Gauge32
       UNITS           "octets"
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "The maximum congestion window used during Slow Start, in
           octets."
       REFERENCE
          "RFC 2581, TCP Congestion Control"
       ::= { tcpEStatsStackEntry 12 }

   tcpEStatsStackMaxCaCwnd  OBJECT-TYPE
       SYNTAX          Gauge32
       UNITS           "octets"
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "The maximum congestion window used during Congestion
           Avoidance, in octets."
       REFERENCE
          "RFC 2581, TCP Congestion Control"
       ::= { tcpEStatsStackEntry 13 }



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   tcpEStatsStackMaxSsthresh  OBJECT-TYPE
       SYNTAX          Gauge32
       UNITS           "octets"
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "The maximum slow start threshold, excluding the initial
           value."
       REFERENCE
          "RFC 2581, TCP Congestion Control"
       ::= { tcpEStatsStackEntry 14 }

   tcpEStatsStackMinSsthresh  OBJECT-TYPE
       SYNTAX          Gauge32
       UNITS           "octets"
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "The minimum slow start threshold."
       REFERENCE
          "RFC 2581, TCP Congestion Control"
       ::= { tcpEStatsStackEntry 15 }

   tcpEStatsStackInRecovery  OBJECT-TYPE
       SYNTAX          INTEGER {
          tcpESDataContiguous(1),
          tcpESDataUnordered(2),
          tcpESDataRecovery(3)
       }
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "An integer value representing the state of the loss
           recovery for this connection.

           tcpESDataContiguous(1) indicates that the remote receiver
           is reporting contiguous data (no duplicate acknowledgments
           or SACK options) and that there are no unacknowledged
           retransmissions.

           tcpESDataUnordered(2) indicates that the remote receiver is
           reporting missing or out-of-order data (e.g., sending
           duplicate acknowledgments or SACK options) and that there
           are no unacknowledged retransmissions (because the missing
           data has not yet been retransmitted).

           tcpESDataRecovery(3) indicates that the sender has
           outstanding retransmitted data that is still



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           unacknowledged."
       REFERENCE
          "RFC 2581, TCP Congestion Control"
       ::= { tcpEStatsStackEntry 16 }

   tcpEStatsStackDupAcksIn  OBJECT-TYPE
       SYNTAX          ZeroBasedCounter32
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "The number of duplicate ACKs received."
       REFERENCE
          "RFC 2581, TCP Congestion Control"
       ::= { tcpEStatsStackEntry 17 }

   tcpEStatsStackSpuriousFrDetected  OBJECT-TYPE
       SYNTAX          ZeroBasedCounter32
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "The number of acknowledgments reporting out-of-order
           segments after the Fast Retransmit algorithm has already
           retransmitted the segments. (For example as detected by the
           Eifel algorithm).'"
       REFERENCE
          "RFC 3522, The Eifel Detection Algorithm for TCP"
       ::= { tcpEStatsStackEntry 18 }

   tcpEStatsStackSpuriousRtoDetected  OBJECT-TYPE
       SYNTAX          ZeroBasedCounter32
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "The number of acknowledgments reporting segments that have
           already been retransmitted due to a Retransmission Timeout."
       ::= { tcpEStatsStackEntry 19 }

   --
   --  The following optional objects instrument unusual protocol
   --  events that probably indicate implementation problems in
   --  the protocol or path.
   --

   tcpEStatsStackSoftErrors  OBJECT-TYPE
       SYNTAX          ZeroBasedCounter32
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION



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          "The number of segments that fail various consistency tests
           during TCP input processing.  Soft errors might cause the
           segment to be discarded but some do not.  Some of these soft
           errors cause the generation of a TCP acknowledgment, while
           others are silently discarded."
       REFERENCE
          "RFC 793, Transmission Control Protocol"
       ::= { tcpEStatsStackEntry 21 }

   tcpEStatsStackSoftErrorReason  OBJECT-TYPE
       SYNTAX          INTEGER {
          belowDataWindow(1),
          aboveDataWindow(2),
          belowAckWindow(3),
          aboveAckWindow(4),
          belowTSWindow(5),
          aboveTSWindow(6),
          dataCheckSum(7),
          otherSoftError(8)
       }
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "This object identifies which consistency test most recently
           failed during TCP input processing.  This object SHOULD be
           set every time tcpEStatsStackSoftErrors is incremented.  The
           codes are as follows:

           belowDataWindow(1) - All data in the segment is below
           SND.UNA. (Normal for keep-alives and zero window probes).

           aboveDataWindow(2) - Some data in the segment is above
           SND.WND. (Indicates an implementation bug or possible
           attack).

           belowAckWindow(3) - ACK below SND.UNA. (Indicates that the
           return path is reordering ACKs)

           aboveAckWindow(4) - An ACK for data that we have not sent.
           (Indicates an implementation bug or possible attack).

           belowTSWindow(5) - TSecr on the segment is older than the
           current TS.Recent (Normal for the rare case where PAWS
           detects data reordered by the network).

           aboveTSWindow(6) - TSecr on the segment is newer than the
           current TS.Recent. (Indicates an implementation bug or
           possible attack).



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           dataCheckSum(7) - Incorrect checksum.  Note that this value
           is intrinsically fragile, because the header fields used to
           identify the connection may have been corrupted.

           otherSoftError(8) - All other soft errors not listed
           above."
       REFERENCE
          "RFC 793, Transmission Control Protocol"
       ::= { tcpEStatsStackEntry 22 }

   --
   --  The following optional objects expose the detailed
   --  operation of the congestion control algorithms.
   --

   tcpEStatsStackSlowStart  OBJECT-TYPE
       SYNTAX          ZeroBasedCounter32
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "The number of times the congestion window has been
           increased by the Slow Start algorithm."
       REFERENCE
          "RFC 2581, TCP Congestion Control"
       ::= { tcpEStatsStackEntry 23 }

   tcpEStatsStackCongAvoid  OBJECT-TYPE
       SYNTAX          ZeroBasedCounter32
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "The number of times the congestion window has been
           increased by the Congestion Avoidance algorithm."
       REFERENCE
          "RFC 2581, TCP Congestion Control"
       ::= { tcpEStatsStackEntry 24 }

   tcpEStatsStackOtherReductions  OBJECT-TYPE
       SYNTAX          ZeroBasedCounter32
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "The number of congestion window reductions made as a result
           of anything other than AIMD congestion control algorithms.
           Examples of non-multiplicative window reductions include
           Congestion Window Validation [RFC2861] and experimental
           algorithms such as Vegas [Bra94].



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           All window reductions MUST be counted as either
           tcpEStatsPerfCongSignals or tcpEStatsStackOtherReductions."
       REFERENCE
          "RFC 2861, TCP Congestion Window Validation"
       ::= { tcpEStatsStackEntry 25 }

   tcpEStatsStackCongOverCount  OBJECT-TYPE
       SYNTAX          ZeroBasedCounter32
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "The number of congestion events that were 'backed out' of
           the congestion control state machine such that the
           congestion window was restored to a prior value.  This can
           happen due to the Eifel algorithm [RFC3522] or other
           algorithms that can be used to detect and cancel spurious
           invocations of the Fast Retransmit Algorithm.

           Although it may be feasible to undo the effects of spurious
           invocation of the Fast Retransmit congestion events cannot
           easily be backed out of tcpEStatsPerfCongSignals and
           tcpEStatsPathPreCongSumCwnd, etc."
       REFERENCE
          "RFC 3522, The Eifel Detection Algorithm for TCP"
       ::= { tcpEStatsStackEntry 26 }

   tcpEStatsStackFastRetran  OBJECT-TYPE
       SYNTAX          ZeroBasedCounter32
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "The number of invocations of the Fast Retransmit algorithm."
       REFERENCE
          "RFC 2581, TCP Congestion Control"
       ::= { tcpEStatsStackEntry 27 }

   tcpEStatsStackSubsequentTimeouts  OBJECT-TYPE
       SYNTAX          ZeroBasedCounter32
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "The number of times the retransmit timeout has expired after
           the RTO has been doubled.  See Section 5.5 of RFC 2988."
       REFERENCE
          "RFC 2988, Computing TCP's Retransmission Timer"
       ::= { tcpEStatsStackEntry 28 }




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   tcpEStatsStackCurTimeoutCount  OBJECT-TYPE
       SYNTAX          Gauge32
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "The current number of times the retransmit timeout has
           expired without receiving an acknowledgment for new data.
           tcpEStatsStackCurTimeoutCount is reset to zero when new
           data is acknowledged and incremented for each invocation of
           Section 5.5 of RFC 2988."
       REFERENCE
          "RFC 2988, Computing TCP's Retransmission Timer"
       ::= { tcpEStatsStackEntry 29 }

   tcpEStatsStackAbruptTimeouts  OBJECT-TYPE
       SYNTAX          ZeroBasedCounter32
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "The number of timeouts that occurred without any
           immediately preceding duplicate acknowledgments or other
           indications of congestion.  Abrupt Timeouts indicate that
           the path lost an entire window of data or acknowledgments.

           Timeouts that are preceded by duplicate acknowledgments or
           other congestion signals (e.g., ECN) are not counted as
           abrupt, and might have been avoided by a more sophisticated
           Fast Retransmit algorithm."
       REFERENCE
          "RFC 2581, TCP Congestion Control"
       ::= { tcpEStatsStackEntry 30 }

   tcpEStatsStackSACKsRcvd  OBJECT-TYPE
       SYNTAX          ZeroBasedCounter32
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "The number of SACK options received."
       REFERENCE
          "RFC 2018, TCP Selective Acknowledgement Options"
       ::= { tcpEStatsStackEntry 31 }

   tcpEStatsStackSACKBlocksRcvd  OBJECT-TYPE
       SYNTAX          ZeroBasedCounter32
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "The number of SACK blocks received (within SACK options)."



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       REFERENCE
          "RFC 2018, TCP Selective Acknowledgement Options"
       ::= { tcpEStatsStackEntry 32 }

   tcpEStatsStackSendStall  OBJECT-TYPE
       SYNTAX          ZeroBasedCounter32
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "The number of interface stalls or other sender local
           resource limitations that are treated as congestion
           signals."
       ::= { tcpEStatsStackEntry 33 }

   tcpEStatsStackDSACKDups  OBJECT-TYPE
       SYNTAX          ZeroBasedCounter32
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "The number of duplicate segments reported to the local host
           by D-SACK blocks."
       REFERENCE
          "RFC 2883, An Extension to the Selective Acknowledgement
           (SACK) Option for TCP"
       ::= { tcpEStatsStackEntry 34 }

   --
   --  The following optional objects instrument path MTU
   --  discovery.
   --

   tcpEStatsStackMaxMSS  OBJECT-TYPE
       SYNTAX          Gauge32
       UNITS           "octets"
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "The maximum MSS, in octets."
       REFERENCE
          "RFC 1191, Path MTU discovery"
       ::= { tcpEStatsStackEntry 35 }

   tcpEStatsStackMinMSS  OBJECT-TYPE
       SYNTAX          Gauge32
       UNITS           "octets"
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION



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          "The minimum MSS, in octets."
       REFERENCE
          "RFC 1191, Path MTU discovery"
       ::= { tcpEStatsStackEntry 36 }

   --
   --  The following optional initial value objects are useful for
   --  conformance testing instruments on application progress and
   --  consumed network resources.
   --

   tcpEStatsStackSndInitial  OBJECT-TYPE
       SYNTAX          Unsigned32
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "Initial send sequence number.  Note that by definition
           tcpEStatsStackSndInitial never changes for a given
           connection."
       REFERENCE
          "RFC 793, Transmission Control Protocol"
       ::= { tcpEStatsStackEntry 37 }

   tcpEStatsStackRecInitial  OBJECT-TYPE
       SYNTAX          Unsigned32
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "Initial receive sequence number.  Note that by definition
           tcpEStatsStackRecInitial never changes for a given
           connection."
       REFERENCE
          "RFC 793, Transmission Control Protocol"
       ::= { tcpEStatsStackEntry 38 }

   --
   --  The following optional objects instrument the senders
   --  buffer usage, including any buffering in the application
   --  interface to TCP and the retransmit queue.  All 'buffer
   --  memory' instruments are assumed to include OS data
   --  structure overhead.
   --

   tcpEStatsStackCurRetxQueue  OBJECT-TYPE
       SYNTAX          Gauge32
       UNITS           "octets"
       MAX-ACCESS      read-only
       STATUS          current



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       DESCRIPTION
          "The current number of octets of data occupying the
           retransmit queue."
       ::= { tcpEStatsStackEntry 39 }

   tcpEStatsStackMaxRetxQueue  OBJECT-TYPE
       SYNTAX          Gauge32
       UNITS           "octets"
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "The maximum number of octets of data occupying the
           retransmit queue."
       ::= { tcpEStatsStackEntry 40 }

   tcpEStatsStackCurReasmQueue  OBJECT-TYPE
       SYNTAX          Gauge32
       UNITS           "octets"
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "The current number of octets of sequence space spanned by
           the reassembly queue.  This is generally the difference
           between rcv.nxt and the sequence number of the right most
           edge of the reassembly queue."
       ::= { tcpEStatsStackEntry 41 }

   tcpEStatsStackMaxReasmQueue  OBJECT-TYPE
       SYNTAX          Gauge32
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "The maximum value of tcpEStatsStackCurReasmQueue"
       ::= { tcpEStatsStackEntry 42 }

   -- ================================================================
   --
   -- Statistics for diagnosing interactions between
   -- applications and TCP.
   --

   tcpEStatsAppTable    OBJECT-TYPE
       SYNTAX      SEQUENCE OF TcpEStatsAppEntry
       MAX-ACCESS  not-accessible
       STATUS      current
       DESCRIPTION
           "This table contains objects that are useful for
           determining if the application using TCP is



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           limiting TCP performance.

           Entries are retained in this table for the number of
           seconds indicated by the tcpEStatsConnTableLatency
           object, after the TCP connection first enters the closed
           state."
       ::= { tcpEStats 6 }

   tcpEStatsAppEntry  OBJECT-TYPE
       SYNTAX       TcpEStatsAppEntry
       MAX-ACCESS   not-accessible
       STATUS       current
       DESCRIPTION
           "Each entry in this table has information about the
           characteristics of each active and recently closed TCP
           connection."
      INDEX { tcpEStatsConnectIndex }
      ::= { tcpEStatsAppTable 1 }

   TcpEStatsAppEntry ::= SEQUENCE {

           tcpEStatsAppSndUna                  Counter32,
           tcpEStatsAppSndNxt                  Unsigned32,
           tcpEStatsAppSndMax                  Counter32,
           tcpEStatsAppThruOctetsAcked         ZeroBasedCounter32,
           tcpEStatsAppHCThruOctetsAcked       ZeroBasedCounter64,
           tcpEStatsAppRcvNxt                  Counter32,
           tcpEStatsAppThruOctetsReceived      ZeroBasedCounter32,
           tcpEStatsAppHCThruOctetsReceived    ZeroBasedCounter64,
           tcpEStatsAppCurAppWQueue            Gauge32,
           tcpEStatsAppMaxAppWQueue            Gauge32,
           tcpEStatsAppCurAppRQueue            Gauge32,
           tcpEStatsAppMaxAppRQueue            Gauge32
       }

   --
   --  The following objects provide throughput statistics for the
   --  connection including sequence numbers and elapsed
   --  application data.  These permit direct observation of the
   --  applications progress, in terms of elapsed data delivery
   --  and elapsed time.
   --

   tcpEStatsAppSndUna  OBJECT-TYPE
       SYNTAX          Counter32
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION



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          "The value of SND.UNA, the oldest unacknowledged sequence
           number.

           Note that SND.UNA is a TCP state variable that is congruent
           to Counter32 semantics."
       REFERENCE
          "RFC 793, Transmission Control Protocol"
       ::= { tcpEStatsAppEntry 1 }

   tcpEStatsAppSndNxt  OBJECT-TYPE
       SYNTAX          Unsigned32
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "The value of SND.NXT, the next sequence number to be sent.
           Note that tcpEStatsAppSndNxt is not monotonic (and thus not
           a counter) because TCP sometimes retransmits lost data by
           pulling tcpEStatsAppSndNxt back to the missing data."
       REFERENCE
          "RFC 793, Transmission Control Protocol"
       ::= { tcpEStatsAppEntry 2 }

   tcpEStatsAppSndMax  OBJECT-TYPE
       SYNTAX          Counter32
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "The farthest forward (right most or largest) SND.NXT value.
           Note that this will be equal to tcpEStatsAppSndNxt except
           when tcpEStatsAppSndNxt is pulled back during recovery."
       REFERENCE
          "RFC 793, Transmission Control Protocol"
       ::= { tcpEStatsAppEntry 3 }

   tcpEStatsAppThruOctetsAcked  OBJECT-TYPE
       SYNTAX          ZeroBasedCounter32
       UNITS           "octets"
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "The number of octets for which cumulative acknowledgments
           have been received.  Note that this will be the sum of
           changes to tcpEStatsAppSndUna."
       ::= { tcpEStatsAppEntry 4 }

   tcpEStatsAppHCThruOctetsAcked  OBJECT-TYPE
       SYNTAX          ZeroBasedCounter64
       UNITS           "octets"



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       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "The number of octets for which cumulative acknowledgments
           have been received, on systems that can receive more than
           10 million bits per second.  Note that this will be the sum
           of changes in tcpEStatsAppSndUna."
       ::= { tcpEStatsAppEntry 5 }

   tcpEStatsAppRcvNxt  OBJECT-TYPE
       SYNTAX          Counter32
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "The value of RCV.NXT.  The next sequence number expected on
           an incoming segment, and the left or lower edge of the
           receive window.

           Note that RCV.NXT is a TCP state variable that is congruent
           to Counter32 semantics."
       REFERENCE
          "RFC 793, Transmission Control Protocol"
       ::= { tcpEStatsAppEntry 6 }

   tcpEStatsAppThruOctetsReceived  OBJECT-TYPE
       SYNTAX          ZeroBasedCounter32
       UNITS           "octets"
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "The number of octets for which cumulative acknowledgments
           have been sent.  Note that this will be the sum of changes
           to tcpEStatsAppRcvNxt."
       ::= { tcpEStatsAppEntry 7 }

   tcpEStatsAppHCThruOctetsReceived  OBJECT-TYPE
       SYNTAX          ZeroBasedCounter64
       UNITS           "octets"
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "The number of octets for which cumulative acknowledgments
           have been sent, on systems that can transmit more than 10
           million bits per second.  Note that this will be the sum of
           changes in tcpEStatsAppRcvNxt."
       ::= { tcpEStatsAppEntry 8 }

   tcpEStatsAppCurAppWQueue  OBJECT-TYPE



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       SYNTAX          Gauge32
       UNITS           "octets"
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "The current number of octets of application data buffered
           by TCP, pending first transmission, i.e., to the left of
           SND.NXT or SndMax.  This data will generally be transmitted
           (and SND.NXT advanced to the left) as soon as there is an
           available congestion window (cwnd) or receiver window
           (rwin).  This is the amount of data readily available for
           transmission, without scheduling the application.  TCP
           performance may suffer if there is insufficient queued
           write data."
       ::= { tcpEStatsAppEntry 11 }

   tcpEStatsAppMaxAppWQueue  OBJECT-TYPE
       SYNTAX          Gauge32
       UNITS           "octets"
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "The maximum number of octets of application data buffered
           by TCP, pending first transmission.  This is the maximum
           value of tcpEStatsAppCurAppWQueue.  This pair of objects can
           be used to determine if insufficient queued data is steady
           state (suggesting insufficient queue space) or transient
           (suggesting insufficient application performance or
           excessive CPU load or scheduler latency)."
       ::= { tcpEStatsAppEntry 12 }

   tcpEStatsAppCurAppRQueue  OBJECT-TYPE
       SYNTAX          Gauge32
       UNITS           "octets"
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION
          "The current number of octets of application data that has
           been acknowledged by TCP but not yet delivered to the
           application."
       ::= { tcpEStatsAppEntry 13 }

   tcpEStatsAppMaxAppRQueue  OBJECT-TYPE
       SYNTAX          Gauge32
       UNITS           "octets"
       MAX-ACCESS      read-only
       STATUS          current
       DESCRIPTION



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          "The maximum number of octets of application data that has
           been acknowledged by TCP but not yet delivered to the
           application."
       ::= { tcpEStatsAppEntry 14 }

   -- ================================================================
   --
   -- Controls for Tuning TCP
   --

   tcpEStatsTuneTable    OBJECT-TYPE
       SYNTAX      SEQUENCE OF TcpEStatsTuneEntry
       MAX-ACCESS  not-accessible
       STATUS      current
       DESCRIPTION
           "This table contains per-connection controls that can
           be used to work around a number of common problems that
           plague TCP over some paths.  All can be characterized as
           limiting the growth of the congestion window so as to
           prevent TCP from overwhelming some component in the
           path.

           Entries are retained in this table for the number of
           seconds indicated by the tcpEStatsConnTableLatency
           object, after the TCP connection first enters the closed
           state."
       ::= { tcpEStats 7 }

   tcpEStatsTuneEntry  OBJECT-TYPE
       SYNTAX       TcpEStatsTuneEntry
       MAX-ACCESS   not-accessible
       STATUS       current
       DESCRIPTION
           "Each entry in this table is a control that can be used to
           place limits on each active TCP connection."
      INDEX { tcpEStatsConnectIndex }
      ::= { tcpEStatsTuneTable 1 }

   TcpEStatsTuneEntry ::= SEQUENCE {

           tcpEStatsTuneLimCwnd                Unsigned32,
           tcpEStatsTuneLimSsthresh            Unsigned32,
           tcpEStatsTuneLimRwin                Unsigned32,
           tcpEStatsTuneLimMSS                 Unsigned32
       }

   tcpEStatsTuneLimCwnd  OBJECT-TYPE
       SYNTAX          Unsigned32



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       UNITS           "octets"
       MAX-ACCESS      read-write
       STATUS          current
       DESCRIPTION
          "A control to set the maximum congestion window that may be
           used, in octets."
       REFERENCE
          "RFC 2581, TCP Congestion Control"
       ::= { tcpEStatsTuneEntry 1 }

   tcpEStatsTuneLimSsthresh  OBJECT-TYPE
       SYNTAX          Unsigned32
       UNITS           "octets"
       MAX-ACCESS      read-write
       STATUS          current
       DESCRIPTION
          "A control to limit the maximum queue space (in octets) that
           this TCP connection is likely to occupy during slowstart.

           It can be implemented with the algorithm described in
           RFC 3742 by setting the max_ssthresh parameter to twice
           tcpEStatsTuneLimSsthresh.

           This algorithm can be used to overcome some TCP performance
           problems over network paths that do not have sufficient
           buffering to withstand the bursts normally present during
           slowstart."
       REFERENCE
          "RFC 3742, Limited Slow-Start for TCP with Large Congestion
           Windows"
       ::= { tcpEStatsTuneEntry 2 }

   tcpEStatsTuneLimRwin  OBJECT-TYPE
       SYNTAX          Unsigned32
       UNITS           "octets"
       MAX-ACCESS      read-write
       STATUS          current
       DESCRIPTION
          "A control to set the maximum window advertisement that may
           be sent, in octets."
       REFERENCE
          "RFC 793, Transmission Control Protocol"
       ::= { tcpEStatsTuneEntry 3 }

   tcpEStatsTuneLimMSS  OBJECT-TYPE
       SYNTAX          Unsigned32
       UNITS           "octets"
       MAX-ACCESS      read-write



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       STATUS          current
       DESCRIPTION
          "A control to limit the maximum segment size in octets, that
           this TCP connection can use."
       REFERENCE
          "RFC 1191, Path MTU discovery"
       ::= { tcpEStatsTuneEntry 4 }

   -- ================================================================
   --
   -- TCP Extended Statistics Notifications Group
   --

   tcpEStatsEstablishNotification NOTIFICATION-TYPE
       OBJECTS     {
                     tcpEStatsConnectIndex
                   }
       STATUS      current
       DESCRIPTION
           "The indicated connection has been accepted
           (or alternatively entered the established state)."
       ::= { tcpEStatsNotifications 1 }

   tcpEStatsCloseNotification NOTIFICATION-TYPE
       OBJECTS     {
                     tcpEStatsConnectIndex
                   }
       STATUS      current
       DESCRIPTION
           "The indicated connection has left the
           established state"
       ::= { tcpEStatsNotifications 2 }

   -- ================================================================
   --
   -- Conformance Definitions
   --

      tcpEStatsCompliances   OBJECT IDENTIFIER
           ::= { tcpEStatsConformance 1 }
      tcpEStatsGroups        OBJECT IDENTIFIER
           ::= { tcpEStatsConformance 2 }

   --
   -- Compliance Statements
   --

     tcpEStatsCompliance MODULE-COMPLIANCE



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        STATUS current
        DESCRIPTION
            "Compliance statement for all systems that implement TCP
            extended statistics."
        MODULE -- this module
            MANDATORY-GROUPS {
                               tcpEStatsListenerGroup,
                               tcpEStatsConnectIdGroup,
                               tcpEStatsPerfGroup,
                               tcpEStatsPathGroup,
                               tcpEStatsStackGroup,
                               tcpEStatsAppGroup
                             }
            GROUP tcpEStatsListenerHCGroup
            DESCRIPTION
                "This group is mandatory for all systems that can
                 wrap the values of the 32-bit counters in
                 tcpEStatsListenerGroup in less than one hour."

            GROUP tcpEStatsPerfOptionalGroup
            DESCRIPTION
                "This group is optional for all systems."

            GROUP tcpEStatsPerfHCGroup
            DESCRIPTION
                "This group is mandatory for systems that can
                wrap the values of the 32-bit counters in
                tcpEStatsPerfGroup in less than one hour.

                Note that any system that can attain 10 Mb/s
                can potentially wrap 32-Bit Octet counters in
                under one hour."

            GROUP tcpEStatsPathOptionalGroup
            DESCRIPTION
                "This group is optional for all systems."

            GROUP tcpEStatsPathHCGroup
            DESCRIPTION
                "This group is mandatory for systems that can
                wrap the values of the 32-bit counters in
                tcpEStatsPathGroup in less than one hour.

                Note that any system that can attain 10 Mb/s
                can potentially wrap 32-Bit Octet counters in
                under one hour."

            GROUP tcpEStatsStackOptionalGroup



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            DESCRIPTION
                "This group is optional for all systems."

            GROUP tcpEStatsAppHCGroup
            DESCRIPTION
                "This group is mandatory for systems that can
                wrap the values of the 32-bit counters in
                tcpEStatsStackGroup in less than one hour.

                Note that any system that can attain 10 Mb/s
                can potentially wrap 32-Bit Octet counters in
                under one hour."

            GROUP tcpEStatsAppOptionalGroup
            DESCRIPTION
                "This group is optional for all systems."

            GROUP tcpEStatsTuneOptionalGroup
            DESCRIPTION
                "This group is optional for all systems."

            GROUP tcpEStatsNotificationsGroup
            DESCRIPTION
                "This group is optional for all systems."

            GROUP tcpEStatsNotificationsCtlGroup
            DESCRIPTION
                "This group is mandatory for systems that include the
                 tcpEStatsNotificationGroup."

      ::= { tcpEStatsCompliances 1 }

   -- ================================================================
   --
   -- Units of Conformance
   --
       tcpEStatsListenerGroup  OBJECT-GROUP
            OBJECTS {
                 tcpEStatsListenerTableLastChange,
                 tcpEStatsListenerStartTime,
                 tcpEStatsListenerSynRcvd,
                 tcpEStatsListenerInitial,
                 tcpEStatsListenerEstablished,
                 tcpEStatsListenerAccepted,
                 tcpEStatsListenerExceedBacklog,
                 tcpEStatsListenerCurConns,
                 tcpEStatsListenerMaxBacklog,
                 tcpEStatsListenerCurBacklog,



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                 tcpEStatsListenerCurEstabBacklog
            }
            STATUS current
            DESCRIPTION
                 "The tcpEStatsListener group includes objects that
                 provide valuable statistics and debugging
                 information for TCP Listeners."
         ::= { tcpEStatsGroups 1 }

       tcpEStatsListenerHCGroup  OBJECT-GROUP
            OBJECTS {
                 tcpEStatsListenerHCSynRcvd,
                 tcpEStatsListenerHCInitial,
                 tcpEStatsListenerHCEstablished,
                 tcpEStatsListenerHCAccepted,
                 tcpEStatsListenerHCExceedBacklog
            }
            STATUS current
            DESCRIPTION
                 "The tcpEStatsListenerHC group includes 64-bit
                  counters in tcpEStatsListenerTable."
         ::= { tcpEStatsGroups 2 }

       tcpEStatsConnectIdGroup  OBJECT-GROUP
            OBJECTS {
                 tcpEStatsConnTableLatency,
                 tcpEStatsConnectIndex
            }
            STATUS current
            DESCRIPTION
                 "The tcpEStatsConnectId group includes objects that
                 identify TCP connections and control how long TCP
                 connection entries are retained in the tables."
         ::= { tcpEStatsGroups 3 }

       tcpEStatsPerfGroup  OBJECT-GROUP
            OBJECTS {
                 tcpEStatsPerfSegsOut, tcpEStatsPerfDataSegsOut,
                 tcpEStatsPerfDataOctetsOut,
                 tcpEStatsPerfSegsRetrans,
                 tcpEStatsPerfOctetsRetrans, tcpEStatsPerfSegsIn,
                 tcpEStatsPerfDataSegsIn,
                 tcpEStatsPerfDataOctetsIn,
                 tcpEStatsPerfElapsedSecs,
                 tcpEStatsPerfElapsedMicroSecs,
                 tcpEStatsPerfStartTimeStamp, tcpEStatsPerfCurMSS,
                 tcpEStatsPerfPipeSize, tcpEStatsPerfMaxPipeSize,
                 tcpEStatsPerfSmoothedRTT, tcpEStatsPerfCurRTO,



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                 tcpEStatsPerfCongSignals, tcpEStatsPerfCurCwnd,
                 tcpEStatsPerfCurSsthresh, tcpEStatsPerfTimeouts,
                 tcpEStatsPerfCurRwinSent,
                 tcpEStatsPerfMaxRwinSent,
                 tcpEStatsPerfZeroRwinSent,
                 tcpEStatsPerfCurRwinRcvd,
                 tcpEStatsPerfMaxRwinRcvd,
                 tcpEStatsPerfZeroRwinRcvd
            }
            STATUS current
            DESCRIPTION
                 "The tcpEStatsPerf group includes those objects that
                 provide basic performance data for a TCP connection."
         ::= { tcpEStatsGroups 4 }

       tcpEStatsPerfOptionalGroup  OBJECT-GROUP
            OBJECTS {
                 tcpEStatsPerfSndLimTransRwin,
                 tcpEStatsPerfSndLimTransCwnd,
                 tcpEStatsPerfSndLimTransSnd,
                 tcpEStatsPerfSndLimTimeRwin,
                 tcpEStatsPerfSndLimTimeCwnd,
                 tcpEStatsPerfSndLimTimeSnd
            }
            STATUS current
            DESCRIPTION
                 "The tcpEStatsPerf group includes those objects that
                 provide basic performance data for a TCP connection."
         ::= { tcpEStatsGroups 5 }

       tcpEStatsPerfHCGroup  OBJECT-GROUP
            OBJECTS {
                 tcpEStatsPerfHCDataOctetsOut,
                 tcpEStatsPerfHCDataOctetsIn
            }
            STATUS current
            DESCRIPTION
                 "The tcpEStatsPerfHC group includes 64-bit
                 counters in the tcpEStatsPerfTable."
         ::= { tcpEStatsGroups 6 }


       tcpEStatsPathGroup  OBJECT-GROUP
            OBJECTS {
                 tcpEStatsControlPath,
                 tcpEStatsPathRetranThresh,
                 tcpEStatsPathNonRecovDAEpisodes,
                 tcpEStatsPathSumOctetsReordered,



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                 tcpEStatsPathNonRecovDA
            }
            STATUS current
            DESCRIPTION
                 "The tcpEStatsPath group includes objects that
                 control the creation of the tcpEStatsPathTable,
                 and provide information about the path
                 for each TCP connection."
         ::= { tcpEStatsGroups 7 }

       tcpEStatsPathOptionalGroup  OBJECT-GROUP
            OBJECTS {
                 tcpEStatsPathSampleRTT, tcpEStatsPathRTTVar,
                 tcpEStatsPathMaxRTT, tcpEStatsPathMinRTT,
                 tcpEStatsPathSumRTT, tcpEStatsPathCountRTT,
                 tcpEStatsPathMaxRTO, tcpEStatsPathMinRTO,
                 tcpEStatsPathIpTtl, tcpEStatsPathIpTosIn,
                 tcpEStatsPathIpTosOut,
                 tcpEStatsPathPreCongSumCwnd,
                 tcpEStatsPathPreCongSumRTT,
                 tcpEStatsPathPostCongSumRTT,
                 tcpEStatsPathPostCongCountRTT,
                 tcpEStatsPathECNsignals,
                 tcpEStatsPathDupAckEpisodes, tcpEStatsPathRcvRTT,
                 tcpEStatsPathDupAcksOut, tcpEStatsPathCERcvd,
                 tcpEStatsPathECESent
            }
            STATUS current
            DESCRIPTION
                 "The tcpEStatsPath group includes objects that
                 provide additional information about the path
                 for each TCP connection."
         ::= { tcpEStatsGroups 8 }

     tcpEStatsPathHCGroup  OBJECT-GROUP
            OBJECTS {
                 tcpEStatsPathHCSumRTT
            }
            STATUS current
            DESCRIPTION
                 "The tcpEStatsPathHC group includes 64-bit
                 counters in the tcpEStatsPathTable."
         ::= { tcpEStatsGroups 9 }

       tcpEStatsStackGroup  OBJECT-GROUP
            OBJECTS {
                 tcpEStatsControlStack,
                 tcpEStatsStackActiveOpen, tcpEStatsStackMSSSent,



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                 tcpEStatsStackMSSRcvd, tcpEStatsStackWinScaleSent,
                 tcpEStatsStackWinScaleRcvd,
                 tcpEStatsStackTimeStamps, tcpEStatsStackECN,
                 tcpEStatsStackWillSendSACK,
                 tcpEStatsStackWillUseSACK, tcpEStatsStackState,
                 tcpEStatsStackNagle, tcpEStatsStackMaxSsCwnd,
                 tcpEStatsStackMaxCaCwnd,
                 tcpEStatsStackMaxSsthresh,
                 tcpEStatsStackMinSsthresh,
                 tcpEStatsStackInRecovery, tcpEStatsStackDupAcksIn,
                 tcpEStatsStackSpuriousFrDetected,
                 tcpEStatsStackSpuriousRtoDetected
            }
            STATUS current
            DESCRIPTION
                 "The tcpEStatsConnState group includes objects that
                 control the creation of the tcpEStatsStackTable,
                 and provide information about the operation of
                 algorithms used within TCP."
         ::= { tcpEStatsGroups 10 }

       tcpEStatsStackOptionalGroup  OBJECT-GROUP
            OBJECTS {
                 tcpEStatsStackSoftErrors,
                 tcpEStatsStackSoftErrorReason,
                 tcpEStatsStackSlowStart, tcpEStatsStackCongAvoid,
                 tcpEStatsStackOtherReductions,
                 tcpEStatsStackCongOverCount,
                 tcpEStatsStackFastRetran,
                 tcpEStatsStackSubsequentTimeouts,
                 tcpEStatsStackCurTimeoutCount,
                 tcpEStatsStackAbruptTimeouts,
                 tcpEStatsStackSACKsRcvd,
                 tcpEStatsStackSACKBlocksRcvd,
                 tcpEStatsStackSendStall, tcpEStatsStackDSACKDups,
                 tcpEStatsStackMaxMSS, tcpEStatsStackMinMSS,
                 tcpEStatsStackSndInitial,
                 tcpEStatsStackRecInitial,
                 tcpEStatsStackCurRetxQueue,
                 tcpEStatsStackMaxRetxQueue,
                 tcpEStatsStackCurReasmQueue,
                 tcpEStatsStackMaxReasmQueue
            }
            STATUS current
            DESCRIPTION
                 "The tcpEStatsConnState group includes objects that
                 provide additional information about the operation of
                 algorithms used within TCP."



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         ::= { tcpEStatsGroups 11 }

       tcpEStatsAppGroup  OBJECT-GROUP
            OBJECTS {
                 tcpEStatsControlApp,
                 tcpEStatsAppSndUna, tcpEStatsAppSndNxt,
                 tcpEStatsAppSndMax, tcpEStatsAppThruOctetsAcked,
                 tcpEStatsAppRcvNxt,
                 tcpEStatsAppThruOctetsReceived
            }
            STATUS current
            DESCRIPTION
                 "The tcpEStatsConnState group includes objects that
                 control the creation of the tcpEStatsAppTable,
                 and provide information about the operation of
                 algorithms used within TCP."
         ::= { tcpEStatsGroups 12 }

     tcpEStatsAppHCGroup  OBJECT-GROUP
            OBJECTS {
                 tcpEStatsAppHCThruOctetsAcked,
                 tcpEStatsAppHCThruOctetsReceived
            }
            STATUS current
            DESCRIPTION
                 "The tcpEStatsStackHC group includes 64-bit
                 counters in the tcpEStatsStackTable."
         ::= { tcpEStatsGroups 13 }

       tcpEStatsAppOptionalGroup  OBJECT-GROUP
            OBJECTS {
                 tcpEStatsAppCurAppWQueue,
                 tcpEStatsAppMaxAppWQueue,
                 tcpEStatsAppCurAppRQueue,
                 tcpEStatsAppMaxAppRQueue
            }
            STATUS current
            DESCRIPTION
                 "The tcpEStatsConnState group includes objects that
                 provide additional information about how applications
                 are interacting with each TCP connection."
         ::= { tcpEStatsGroups 14 }

       tcpEStatsTuneOptionalGroup  OBJECT-GROUP
            OBJECTS {
                 tcpEStatsControlTune,
                 tcpEStatsTuneLimCwnd, tcpEStatsTuneLimSsthresh,
                 tcpEStatsTuneLimRwin, tcpEStatsTuneLimMSS



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            }
            STATUS current
            DESCRIPTION
                 "The tcpEStatsConnState group includes objects that
                 control the creation of the tcpEStatsConnectionTable,
                 which can be used to set tuning parameters
                 for each TCP connection."
         ::= { tcpEStatsGroups 15 }

       tcpEStatsNotificationsGroup      NOTIFICATION-GROUP
            NOTIFICATIONS {
                          tcpEStatsEstablishNotification,
                          tcpEStatsCloseNotification
            }
            STATUS   current
            DESCRIPTION
                "Notifications sent by a TCP extended statistics agent."
         ::= { tcpEStatsGroups 16 }

       tcpEStatsNotificationsCtlGroup  OBJECT-GROUP
            OBJECTS {
                          tcpEStatsControlNotify
            }
            STATUS   current
            DESCRIPTION
                "The tcpEStatsNotificationsCtl group includes the
                 object that controls the creation of the events
                 in the tcpEStatsNotificationsGroup."
         ::= { tcpEStatsGroups 17 }

      END




















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5.  Security Considerations

   There are a number of management objects defined in this MIB module
   with a MAX-ACCESS clause of read-write and/or read-create.  Such
   objects may be considered sensitive or vulnerable in some network
   environments.  The support for SET operations in a non-secure
   environment without proper protection can have a negative effect on
   network operations.  These are the tables and objects and their
   sensitivity/vulnerability:

   *  Changing tcpEStatsConnTableLatency or any of the control objects
      in the tcpEStatsControl group (tcpEStatsControlPath,
      tcpEStatsControlStack, tcpEStatsControlApp, tcpEStatsControlTune)
      may affect the correctness of other management applications
      accessing this MIB.  Generally, local policy should only permit
      limited write access to these controls (e.g., only by one
      management station or only during system configuration).

   *  The objects in the tcpEStatsControlTune group
      (tcpEStatsTuneLimCwnd, tcpEStatsTuneLimSsthresh,
      tcpEStatsTuneLimRwin) can be used to limit resources consumed by
      TCP connections or to limit TCP throughput.  An attacker might
      manipulate these objects to reduce performance to levels below the
      minimum acceptable for a particular application.

   Some of the readable objects in this MIB module (i.e., objects with a
   MAX-ACCESS other than not-accessible) may be considered sensitive or
   vulnerable in some network environments.  It is thus important to
   control even GET and/or NOTIFY access to these objects and possibly
   to even encrypt the values of these objects when sending them over
   the network via SNMP.  These are the tables and objects and their
   sensitivity/vulnerability:

   *  All objects which expose TCP sequence numbers (tcpEStatsAppSndUna,
      tcpEStatsAppSndNxt, tcpEStatsAppSndMax, tcpEStatsStackSndInitial,
      tcpEStatsAppRcvNxt, and tcpEStatsStackRecInitial) might make it
      easier for an attacker to forge in sequence TCP segments to
      disrupt TCP connections.

   *  Nearly all objects in this (or any other) MIB may be used to
      estimate traffic volumes, which may reveal unanticipated
      information about an organization to the outside world.

   SNMP versions prior to SNMPv3 did not include adequate security.
   Even if the network itself is secure (for example by using IPsec),
   even then, there is no control as to who on the secure network is
   allowed to access and GET/SET (read/change/create/delete) the objects
   in this MIB module.



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   It is RECOMMENDED that implementers consider the security features as
   provided by the SNMPv3 framework (see [RFC3410], section 8),
   including full support for the SNMPv3 cryptographic mechanisms (for
   authentication and privacy).

   Further, deployment of SNMP versions prior to SNMPv3 is NOT
   RECOMMENDED.  Instead, it is RECOMMENDED to deploy SNMPv3 and to
   enable cryptographic security.  It is then a customer/operator
   responsibility to ensure that the SNMP entity giving access to an
   instance of this MIB module is properly configured to give access to
   the objects only to those principals (users) that have legitimate
   rights to indeed GET or SET (change/create/delete) them.

6.  IANA Considerations

   The MIB module in this document uses the following IANA-assigned
   OBJECT IDENTIFIER values recorded in the SMI Numbers registry:

          Descriptor        OBJECT IDENTIFIER value
          ------------      -----------------------
          tcpEStatsMIB      { mib-2 156 }

7.  Normative References

   [RFC791]   Postel, J., "Internet Protocol", STD 5, RFC 791, September
              1981.

   [RFC793]   Postel, J., "Transmission Control Protocol", STD 7, RFC
              793, September 1981.

   [RFC1122]  Braden, R., Ed., "Requirements for Internet Hosts -
              Communication Layers", STD 3, RFC 1122, October 1989.

   [RFC1191]  Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191,
              November 1990.

   [RFC1323]  Jacobson, V., Braden, R., and D. Borman, "TCP Extensions
              for High Performance", RFC 1323, May 1992.

   [RFC2018]  Mathis, M., Mahdavi, J., Floyd, S., and A. Romanow, "TCP
              Selective Acknowledgment Options", RFC 2018, October 1996.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.







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   [RFC2578]  McCloghrie, K., Perkins, D., Schoenwaelder, J., Case, J.,
              Rose, M., and S. Waldbusser, "Structure of Management
              Information Version 2 (SMIv2)", STD 58, RFC 2578, April
              1999.

   [RFC2579]  McCloghrie, K., Perkins, D., Schoenwaelder, J., Case, J.,
              Rose, M., and S. Waldbusser, "Textual Conventions for
              SMIv2", RFC 2579, STD 58, April 1999.

   [RFC2580]  McCloghrie, K., Perkins, D., Schoenwaelder, J., Case, J.,
              Rose, M., and S. Waldbusser, "Conformance Statements for
              SMIv2", RFC 2580, STD 58, April 1999.

   [RFC2581]  Allman, M., Paxson, V., and W. Stevens, "TCP Congestion
              Control", RFC 2581, April 1999.

   [RFC2856]  Bierman, A., McCloghrie, K., and R. Presuhn, "Textual
              Conventions for Additional High Capacity Data Types", RFC
              2856, June 2000.

   [RFC2883]  Floyd, S., Mahdavi, J., Mathis, M., and M. Podolsky, "An
              Extension to the Selective Acknowledgement (SACK) Option
              for TCP", RFC 2883, July 2000.

   [RFC2988]  Paxson, V. and M. Allman, "Computing TCP's Retransmission
              Timer", RFC 2988, November 2000.

   [RFC3168]  Ramakrishnan, K., Floyd, S., and D. Black, "The Addition
              of Explicit Congestion Notification (ECN) to IP", RFC
              3168, September 2001.

   [RFC3517]  Blanton, E., Allman, M., Fall, K., and L. Wang, "A
              Conservative Selective Acknowledgment (SACK)-based Loss
              Recovery Algorithm for TCP", RFC 3517, April 2003.

   [RFC4022]  Raghunarayan, R., Ed., "Management Information Base for
              the Transmission Control Protocol (TCP)", RFC 4022, March
              2005.

   [RFC4502]  Waldbusser, S., "Remote Network Monitoring Management
              Information Base Version 2", RFC 4502, May 2006.










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8.  Informative References

   [Mat97]    M. Mathis, J. Semke, J. Mahdavi, T. Ott, "The Macroscopic
              Behavior of the TCP Congestion Avoidance Algorithm",
              Computer Communication Review, volume 27, number 3, July
              1997.

   [Bra94]    Brakmo, L., O'Malley, S., "TCP Vegas, New Techniques for
              Congestion Detection and Avoidance", SIGCOMM'94, London,
              pp 24-35, October 1994.

   [Edd06]    Eddy, W., "TCP SYN Flooding Attacks and Common
              Mitigations", Work in Progress, May 2007.

   [POSIX]    Portable Operating System Interface, IEEE Std 1003.1

   [Pad98]    Padhye, J., Firoiu, V., Towsley, D., Kurose, J., "Modeling
              TCP Throughput: A Simple Model and its Empirical
              Validation", SIGCOMM'98.

   [Web100]   Mathis, M., J. Heffner, R. Reddy, "Web100: Extended TCP
              Instrumentation for Research, Education and Diagnosis",
              ACM Computer Communications Review, Vol 33, Num 3, July
              2003.

   [RFC2861]  Handley, M., Padhye, J., and S. Floyd, "TCP Congestion
              Window Validation", RFC 2861, June 2000.

   [RFC3260]  Grossman, D., "New Terminology and Clarifications for
              Diffserv", RFC 3260, April 2002.

   [RFC3410]  Case, J., Mundy, R., Partain, D. and B. Stewart,
              "Introduction and Applicability Statements for Internet-
              Standard Management Framework", RFC 3410, December 2002.

   [RFC3522]  Ludwig, R. and M. Meyer, "The Eifel Detection Algorithm
              for TCP", RFC 3522, April 2003.

   [RFC3742]  Floyd, S., "Limited Slow-Start for TCP with Large
              Congestion Windows", RFC 3742, March 2004.

   [RFC4614]  Duke M., Braden, R., Eddy, W., Blanton, E.  "A Roadmap for
              Transmission Control Protocol (TCP) Specification
              Documents", RFC 4614, September 2006.







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9.  Contributors

   The following people contributed text that was incorporated into this
   document:

   Jon Saperia <saperia@jdscons.com> converted Web100 internal
   documentation into a true MIB.

   Some of the objects in this document were moved from an early version
   of the TCP-MIB by Bill Fenner, et al.

   Some of the object descriptions are based on an earlier unpublished
   document by Jeff Semke.

10.  Acknowledgments

   This document is a product of the Web100 project (www.web100.org), a
   joint effort of Pittsburgh Supercomputing Center (www.psc.edu),
   National Center for Atmospheric Research (www.ncar.ucar.edu), and
   National Center for Supercomputer Applications (www.ncsa.edu).

   It would not have been possible without all of the hard work by the
   entire Web100 team, especially Peter O'Neal, who read and reread the
   entire document several times; Janet Brown and Marla Meehl, who
   patiently managed the unmanageable.  The Web100 project would not
   have been successful without all of the early adopters who suffered
   our bugs to provide many good suggestions and insights into their
   needs for TCP instrumentation.

   Web100 was supported by the National Science Foundation under Grant
   No. 0083285 and a research grant from Cisco Systems.

   We would also like to thank all of the people who built experimental
   implementations of this MIB from early versions and provided us with
   constructive feedback:  Glenn Turner at AARnet, Kristine Adamson at
   IBM, and Xinyan Zan at Microsoft.

   And last, but not least, we would like to thank Dan Romascanu, our
   "MIB Doctor" and Bert Wijnen, the Operations Area Director, for
   patiently steering us through the MIB review process.











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Authors' Addresses

   Matt Mathis
   Pittsburgh Supercomputing Center
   300 S. Craig St.
   Pittsburgh, PA 15213
   Phone: 412-268-4960
   EMail: mathis@psc.edu

   John Heffner
   Pittsburgh Supercomputing Center
   300 S. Craig St.
   Pittsburgh, PA 15213
   Phone: 412-268-4960
   EMail: jheffner@psc.edu

   Rajiv Raghunarayan
   Cisco Systems Inc.
   San Jose, CA 95134
   Phone: 408 853 9612
   EMail: raraghun@cisco.com






























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Full Copyright Statement

   Copyright (C) The IETF Trust (2007).

   This document is subject to the rights, licenses and restrictions
   contained in BCP 78, and except as set forth therein, the authors
   retain all their rights.

   This document and the information contained herein are provided on an
   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
   THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
   OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
   THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Intellectual Property

   The IETF takes no position regarding the validity or scope of any
   Intellectual Property Rights or other rights that might be claimed to
   pertain to the implementation or use of the technology described in
   this document or the extent to which any license under such rights
   might or might not be available; nor does it represent that it has
   made any independent effort to identify any such rights.  Information
   on the procedures with respect to rights in RFC documents can be
   found in BCP 78 and BCP 79.

   Copies of IPR disclosures made to the IETF Secretariat and any
   assurances of licenses to be made available, or the result of an
   attempt made to obtain a general license or permission for the use of
   such proprietary rights by implementers or users of this
   specification can be obtained from the IETF on-line IPR repository at
   http://www.ietf.org/ipr.

   The IETF invites any interested party to bring to its attention any
   copyrights, patents or patent applications, or other proprietary
   rights that may cover technology that may be required to implement
   this standard.  Please address the information to the IETF at
   ietf-ipr@ietf.org.

Acknowledgement

   Funding for the RFC Editor function is currently provided by the
   Internet Society.







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