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draft-ietf-anima-grasp-api-07.txt
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Network Working Group B. E. Carpenter
Internet-Draft Univ. of Auckland
Intended status: Informational B. Liu, Ed.
Expires: 16 April 2021 Huawei Technologies
W. Wang
X. Gong
BUPT University
13 October 2020
Generic Autonomic Signaling Protocol Application Program Interface
(GRASP API)
draft-ietf-anima-grasp-api-07
Abstract
This document is a conceptual outline of an application programming
interface (API) for the Generic Autonomic Signaling Protocol (GRASP).
Such an API is needed for Autonomic Service Agents (ASA) calling the
GRASP protocol module to exchange autonomic network messages with
other ASAs. Since GRASP is designed to support asynchronous
operations, the API will need to be adapted to the support for
asynchronicity in various programming languages and operating
systems.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 16 April 2021.
Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved.
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This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components
extracted from this document must include Simplified BSD License text
as described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. GRASP API for ASA . . . . . . . . . . . . . . . . . . . . . . 4
2.1. Design Assumptions . . . . . . . . . . . . . . . . . . . 4
2.2. Asynchronous Operations . . . . . . . . . . . . . . . . . 5
2.2.1. Alternative Asynchronous Mechanisms . . . . . . . . . 6
2.2.2. Multiple Negotiation Scenario . . . . . . . . . . . . 7
2.2.3. Overlapping Sessions and Operations . . . . . . . . . 8
2.3. API definition . . . . . . . . . . . . . . . . . . . . . 8
2.3.1. Parameters and data structures . . . . . . . . . . . 8
2.3.2. Registration . . . . . . . . . . . . . . . . . . . . 12
2.3.3. Discovery . . . . . . . . . . . . . . . . . . . . . . 15
2.3.4. Negotiation . . . . . . . . . . . . . . . . . . . . . 16
2.3.5. Synchronization and Flooding . . . . . . . . . . . . 21
2.3.6. Invalid Message Function . . . . . . . . . . . . . . 25
3. Implementation Status [RFC Editor: please remove] . . . . . . 26
4. Security Considerations . . . . . . . . . . . . . . . . . . . 26
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 26
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 26
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 26
7.1. Normative References . . . . . . . . . . . . . . . . . . 26
7.2. Informative References . . . . . . . . . . . . . . . . . 26
Appendix A. Error Codes . . . . . . . . . . . . . . . . . . . . 28
Appendix B. Change log [RFC Editor: Please remove] . . . . . . . 29
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 31
1. Introduction
As defined in [I-D.ietf-anima-reference-model], the Autonomic Service
Agent (ASA) is the atomic entity of an autonomic function, and it is
instantiated on autonomic nodes. When ASAs communicate with each
other, they should use the Generic Autonomic Signaling Protocol
(GRASP) [I-D.ietf-anima-grasp].
As Figure 1 shows, a GRASP implementation could contain several sub-
layers. The bottom layer is the GRASP base protocol module, which is
only responsible for sending and receiving GRASP messages and
maintaining shared data structures. Above that is the basic API
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described in this document. The upper layer contains some extended
API functions based upon GRASP basic protocol. For example,
[I-D.ietf-anima-grasp-distribution] describes a possible extended
function.
Multiple ASAs in a single node will share the same instance of GRASP,
much as multiple applications share a single TCP/IP stack. This
aspect is hidden from individual ASAs by the API, and is not further
discussed here.
It is desirable that ASAs can be designed as portable user-space
programs using a system-independent API. In many implementations,
the GRASP code will therefore be split between user space and kernel
space. In user space, library functions provide the API and
communicate directly with ASAs. In kernel space is a daemon, or a
set of sub-services, providing GRASP core functions that are
independent of specific ASAs, such as multicast handling and
relaying, and common data structures such as the discovery cache.
The GRASP API library would need to communicate with the GRASP core
via an inter-process communication (IPC) mechanism. The details of
this are system-dependent.
+--------------+ +--------------+
| ASAs | | ASAs |
+--------------+ +--------------+
| | |
| +------------------+ |
| | GRASP Extended | |
| | Function API | |
| +------------------+ |
| | |
+------------------------------------------+
| GRASP API Library |
+------------------------------------------+
|
IPC
|
+------------------------------------------+
| GRASP Core |
| (functions, data structures, daemon(s)) |
+------------------------------------------+
Figure 1: Software layout
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Both the GRASP library and the extended function modules should be
available to the ASAs. However, since the extended functions are
expected to be added in an incremental manner, they will be the
subject of future documents. This document only describes the basic
GRASP API.
The functions provided by the API do not map one-to-one onto GRASP
messages. Rather, they are intended to offer convenient support for
message sequences (such as a discovery request followed by responses
from several peers, or a negotiation request followed by various
possible responses). This choice was made to assist ASA programmers
in writing code based on their application requirements rather than
needing to understand protocol details.
Note that a simple autonomic node might contain very few ASAs in
addition to the autonomic infrastructure components described in
[I-D.ietf-anima-bootstrapping-keyinfra] and
[I-D.ietf-anima-autonomic-control-plane]. Such a node might directly
integrate a GRASP protocol stack in its code and therefore not
require this API to be installed. However, the programmer would then
need a deeper understanding of the GRASP protocol than is needed to
use the API.
This document gives a conceptual outline of the API. It is not a
formal specification for any particular programming language or
operating system, and it is expected that details will be clarified
in individual implementations.
2. GRASP API for ASA
2.1. Design Assumptions
The assumption of this document is that any Autonomic Service Agent
(ASA) needs to call a GRASP module. The latter handles protocol
details (security, sending and listening for GRASP messages, waiting,
caching discovery results, negotiation looping, sending and receiving
sychronization data, etc.) but understands nothing about individual
GRASP objectives (Section 2.10 of [I-D.ietf-anima-grasp]). The
semantics of objectives are unknown to the GRASP module and are
handled only by the ASAs. Thus, this is an abstract API for use by
ASAs. Individual language bindings should be defined in separate
documents.
Different ASAs may make different use of GRASP features:
* Use GRASP only for discovery purposes.
* Use GRASP negotiation but only as an initiator (client).
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* Use GRASP negotiation but only as a responder.
* Use GRASP negotiation as an initiator or responder.
* Use GRASP synchronization but only as an initiator (recipient).
* Use GRASP synchronization but only as a responder and/or flooder.
* Use GRASP synchronization as an initiator, responder and/or
flooder.
The API also assumes that one ASA may support multiple objectives.
Nothing prevents an ASA from supporting some objectives for
synchronization and others for negotiation.
The API design assumes that the operating system and programming
language provide a mechanism for simultaneous asynchronous
operations. This is discussed in detail in Section 2.2.
A few items are out of scope in this version, since practical
experience is required before including them:
* Authorization of ASAs is not defined as part of GRASP and is not
supported.
* User-supplied explicit locators for an objective are not
supported. The GRASP core will supply the locator, using the ACP
address of the node concerned.
* The Rapid mode of GRASP (Section 2.5.4 of [I-D.ietf-anima-grasp])
is not supported.
2.2. Asynchronous Operations
GRASP depends on asynchronous operations and wait states, and its
messages are not idempotent, meaning that repeating a message may
cause repeated changes of state in the recipient ASA. Many ASAs will
need to support several concurrent operations; for example an ASA
might need to negotiate one objective with a peer while discovering
and synchronizing a different objective with a different peer.
Alternatively, an ASA which acts as a resource manager might need to
run simultaneous negotiations for a given objective with multiple
different peers. Such an ASA will probably need to support
uninterruptible atomic changes to its internal data structures, using
a mechanism provided by the operating system and programming language
in use.
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2.2.1. Alternative Asynchronous Mechanisms
Thus, some ASAs need to support asynchronous operations, and
therefore the GRASP core must do so. Depending on both the operating
system and the programming language in use, there are various
techniques for such parallel operations, three of which we consider
here: multi-threading, an event loop structure using polling, and an
event loop structure using callback functions.
1. In multi-threading, the operating system and language will
provide the necessary support for asynchronous operations,
including creation of new threads, context switching between
threads, queues, locks, and implicit wait states. In this case,
API calls can be treated as simple synchronous function calls
within their own thread, even if the function includes wait
states, blocking and queueing. Concurrent operations will each
run in their own threads. For example, the discover() call may
not return until discovery results have arrived or a timeout has
occurred. If the ASA has other work to do, the discover() call
must be in a thread of its own.
2. In an event loop implementation with polling, blocking calls are
not acceptable. Therefore all calls must be non-blocking, and
the main loop could support multiple GRASP sessions in parallel
by repeatedly polling each one for a change of state. To
facilitate this, the API implementation would provide non-
blocking versions of all the functions that otherwise involve
blocking and queueing. In these calls, a 'noReply' code will be
returned by each call instead of blocking, until such time as the
event for which it is waiting (or a failure) has occurred. Thus,
for example, discover() would return 'noReply' instead of waiting
until discovery has succeeded or timed out. The discover() call
would be repeated in every cycle of the main loop until it
completes. Effectively, it becomes a polling call.
3. In an event loop implementation with callbacks, the ASA
programmer would provide a callback function for each
asynchronous operation, e.g. discovery_received(). This would be
called asynchronously when a reply is received or a failure such
as a timeout occurs.
The following calls involve waiting for a remote operation, so they
could use a polling or callback mechanism. In a threaded mechanism,
they will usually require to be called in a separate thread:
discover() whose callback would be discovery_received().
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request_negotiate() whose callback would be
negotiate_step_received().
negotiate_step() whose callback would be
negotiate_step_received().
listen_negotiate() whose callback would be
negotiate_step_received().
synchronize() whose callback would be synchronization_received().
2.2.2. Multiple Negotiation Scenario
The design of GRASP allows the following scenario. Consider an ASA
"A" that acts as a resource allocator for some objective. An ASA "B"
launches a negotiation with "A" to obtain or release a quantity of
the resource. While this negotatition is under way, "B" chooses to
launch a second simultaneous negotiation with "A" for a different
quantity of the same resource. "A" must therefore conduct two
separate negotiation sessions at the same time with the same peer,
and must not mix them up.
Note that ASAs could be designed to avoid such a scenario, i.e.
restricted to exactly one negotiation session at a time for a given
objective, but this would be a voluntary restriction not required by
the GRASP protocol. In fact it is an assumption of GRASP that any
ASA managing a resource may need to conduct multiple parallel
negotiations, possibly with the same peer. Communication patterns
could be very complex, with a group of ASAs overlapping negotiations
among themselves, as described in [I-D.ciavaglia-anima-coordination].
Therefore, the API design allows for such scenarios.
In the callback model, for the scenario just described, the ASAs "A"
and "B" will each provide two instances of negotiate_step_received(),
one for each session. For this reason, each ASA must be able to
distinguish the two sessions, and the peer's IP address is not
sufficient for this. It is also not safe to rely on transport port
numbers for this, since future variants of GRASP might use shared
ports rather than a separate port per session. Hence the GRASP
design includes a session identifier. Thus, when necessary, a
'session_nonce' parameter is used in the API to distinguish
simultaneous GRASP sessions from each other, so that any number of
sessions may proceed asynchronously in parallel.
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2.2.3. Overlapping Sessions and Operations
On the first call in a new GRASP session, the API returns a
'session_nonce' value based on the GRASP session identifier. This
value must be used in all subsequent calls for the same session, and
will be provided as a parameter in the callback functions. By this
mechanism, multiple overlapping sessions can be distinguished, both
in the ASA and in the GRASP core. The value of the 'session_nonce"
is opaque to the ASA.
An additional mechanism that might increase efficiency for polling
implementations is to add a general call, say notify(), which would
check the status of all outstanding operations for the calling ASA
and return the session_nonce values for all sessions that have
changed state. This would eliminate the need for repeated calls to
the individual functions returning a 'noReply'. This call is not
described below as the details are likely to be implementation-
specific.
An implication of the above for all GRASP implementations is that the
GRASP core must keep state for each GRASP operation in progress, most
likely keyed by the GRASP Session ID and the GRASP source address of
the session initiator. Even in a threaded implementation, the GRASP
core will need such state internally. The session_nonce parameter
exposes this aspect of the implementation.
2.3. API definition
Some example logic flows for a resource management ASA are given in
[I-D.carpenter-anima-asa-guidelines], which may be of help in
understanding the following descriptions. The next section describes
parameters and data structures used in multiple API calls. The
following sections describe various groups of function APIs. Those
APIs that do not list asynchronous mechanisms are implicitly
synchronous in their behaviour.
2.3.1. Parameters and data structures
2.3.1.1. Errorcode
All functions in the API have an unsigned 'errorcode' integer as
their return value (the first returned value in languages that allow
multiple returned parameters). An errorcode of zero indicates
success. Any other value indicates failure of some kind. The first
three errorcodes have special importance:
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1. Declined: used to indicate that the other end has sent a GRASP
Negotiation End message (M_END) with a Decline option
(O_DECLINE).
2. No reply: used in non-blocking calls to indicate that the other
end has sent no reply so far (see Section 2.2).
3. Unspecified error: used when no more specific error code applies.
Appendix A gives a full list of currently suggested error codes,
based on implementation experience. While there is no absolute
requirement for all implementations to use the same error codes, this
is highly recommended for portability of applications.
2.3.1.2. Timeout
Wherever a 'timeout' parameter appears, it is an integer expressed in
milliseconds. If it is zero, the GRASP default timeout
(GRASP_DEF_TIMEOUT, see [I-D.ietf-anima-grasp]) will apply. If no
response is received before the timeout expires, the call will fail
unless otherwise noted.
2.3.1.3. Objective
An 'objective' parameter is a data structure with the following
components:
* name (UTF-8 string) - the objective's name
* neg (Boolean flag) - True if objective supports negotiation
(default False)
* synch (Boolean flag) - True if objective supports synchronization
(default False)
* dry (Boolean flag) - True if objective supports dry-run
negotiation (default False)
- Note 1: Only one of 'synch' or 'neg' may be True.
- Note 2: 'dry' must not be True unless 'neg' is also True.
- Note 3: In a language such as C the preferred implementation
may be to represent the Boolean flags as bits in a single byte.
* loop_count (integer) - Limit on negotiation steps etc. (default
GRASP_DEF_LOOPCT, see [I-D.ietf-anima-grasp])
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* value - a specific data structure expressing the value of the
objective. The format is language dependent, with the constraint
that it can be validly represented in CBOR.
An essential requirement for all language mappings and all
implementations is that, regardless of what other options exist
for a language-specific representation of the value, there is
always an option to use a raw CBOR data item as the value. The
API will then wrap this with CBOR Tag 24 as an encoded CBOR data
item [RFC7049] for transmission via GRASP, and unwrap it after
reception.
The 'name' and 'value' fields are of variable length. GRASP does
not set a maximum length for these fields, but only for the total
length of a GRASP message. Implementations might impose length
limits.
An example data structure definition for an objective in the C
language, assuming the use of a particular CBOR library, is:
typedef struct {
char *name;
uint8_t flags; // flag bits as defined by GRASP
int loop_count;
int value_size; // size of value in bytes
cbor_mutable_data cbor_value;
// CBOR bytestring (libcbor/cbor/data.h)
} objective;
An example data structure definition for an objective in the
Python language is:
class objective:
"""A GRASP objective"""
def __init__(self, name):
self.name = name # Unique name (string)
self.negotiate = False #True if objective supports negotiation
self.dryrun = False #True if objective supports dry-run neg.
self.synch = False # True if objective supports synch
self.loop_count = GRASP_DEF_LOOPCT # Default starting value
self.value = 0 # Place holder; any valid Python object
2.3.1.4. ASA_locator
An 'ASA_locator' parameter is a data structure with the following
contents:
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* locator - The actual locator, either an IP address or an ASCII
string.
* ifi (integer) - The interface identifier index via which this was
discovered - probably no use to a normal ASA
* expire (system dependent type) - The time on the local system
clock when this locator will expire from the cache
* The following cover all locator types currently supported by
GRASP:
- is_ipaddress (Boolean) - True if the locator is an IP address
- is_fqdn (Boolean) - True if the locator is an FQDN
- is_uri (Boolean) - True if the locator is a URI
* diverted (Boolean) - True if the locator was discovered via a
Divert option
* protocol (integer) - Applicable transport protocol (IPPROTO_TCP or
IPPROTO_UDP)
* port (integer) - Applicable port number
The 'locator' field is of variable length in the case of an FQDN or a
URI. GRASP does not set a maximum length for this field, but only
for the total length of a GRASP message. Implementations might
impose length limits.
2.3.1.5. Tagged_objective
A 'tagged_objective' parameter is a data structure with the following
contents:
* objective - An objective
* locator - The ASA_locator associated with the objective, or a null
value.
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2.3.1.6. Asa_nonce
Although an authentication and authorization scheme for ASAs has not
been defined, the API provides a very simple hook for such a scheme.
When an ASA starts up, it registers itself with the GRASP core, which
provides it with an opaque nonce that, although not cryptographically
protected, would be difficult for a third party to predict. The ASA
must present this nonce in future calls. This mechanism will prevent
some elementary errors or trivial attacks such as an ASA manipulating
an objective it has not registered to use.
Thus, in most calls, an 'asa_nonce' parameter is required. It is
generated when an ASA first registers with GRASP, and the ASA must
then store the asa_nonce and use it in every subsequent GRASP call.
Any call in which an invalid nonce is presented will fail. It is an
up to 32-bit opaque value (for example represented as a uint32_t,
depending on the language). It should be unpredictable; a possible
implementation is to use the same mechanism that GRASP uses to
generate Session IDs [I-D.ietf-anima-grasp]. Another possible
implementation is to hash the name of the ASA with a locally defined
secret key.
2.3.1.7. Session_nonce
In some calls, a 'session_nonce' parameter is required. This is an
opaque data structure as far as the ASA is concerned, used to
identify calls to the API as belonging to a specific GRASP session
(see Section 2.2). In fully threaded implementations this parameter
might not be needed, but it is included to act as a session handle if
necessary. It will also allow GRASP to detect and ignore malicious
calls or calls from timed-out sessions. A possible implementation is
to form the nonce from the underlying GRASP Session ID and the source
address of the session.
2.3.2. Registration
These functions are used to register an ASA and the objectives that
it supports with the GRASP module. If an authorization model is
added to GRASP, these API calls would need to be modified
accordingly.
* register_asa()
- Input parameter:
name of the ASA (UTF-8 string)
- Return parameters:
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errorcode (integer)
asa_nonce (integer) (if successful)
- This initialises state in the GRASP module for the calling
entity (the ASA). In the case of success, an 'asa_nonce' is
returned which the ASA must present in all subsequent calls.
In the case of failure, the ASA has not been authorized and
cannot operate.
* deregister_asa()
- Input parameters:
asa_nonce (integer)
name of the ASA (UTF-8 string)
- Return parameter:
errorcode (integer)
- This removes all state in the GRASP module for the calling
entity (the ASA), and deregisters any objectives it has
registered. Note that these actions must also happen
automatically if an ASA crashes.
- Note - the ASA name is strictly speaking redundant in this
call, but is present for clarity.
* register_objective()
- Input parameters:
asa_nonce (integer)
objective (structure)
ttl (integer - default GRASP_DEF_TIMEOUT)
discoverable (Boolean - default False)
overlap (Boolean - default False)
local (Boolean - default False)
- Return parameter:
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errorcode (integer)
- This registers an objective that this ASA supports and may
modify. The 'objective' becomes a candidate for discovery.
However, discovery responses should not be enabled until the
ASA calls listen_negotiate() or listen_synchronize(), showing
that it is able to act as a responder. The ASA may negotiate
the objective or send synchronization or flood data.
Registration is not needed for "read-only" operations, i.e.,
the ASA only wants to receive synchronization or flooded data
for the objective concerned.
- The 'ttl' parameter is the valid lifetime (time to live) in
milliseconds of any discovery response for this objective. The
default value should be the GRASP default timeout
(GRASP_DEF_TIMEOUT, see [I-D.ietf-anima-grasp]).
- If the parameter 'discoverable' is True, the objective is
immediately discoverable. This is intended for objectives that
are only defined for GRASP discovery, and which do not support
negotiation or synchronization.
- If the parameter 'overlap' is True, more than one ASA may
register this objective in the same GRASP instance.
- If the parameter 'local' is True, discovery must return a link-
local address. This feature is for objectives that must be
restricted to the local link.
- This call may be repeated for multiple objectives.
* deregister_objective()
- Input parameters:
asa_nonce (integer)
objective (structure)
- Return parameter:
errorcode (integer)
- The 'objective' must have been registered by the calling ASA;
if not, this call fails. Otherwise, it removes all state in
the GRASP module for the given objective.
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2.3.3. Discovery
* discover()
- Input parameters:
asa_nonce (integer)
objective (structure)
timeout (integer)
age_limit (integer)
- Return parameters:
errorcode (integer)
locator_list (structure)
- This returns a list of discovered 'ASA_locator's for the given
objective. Note that this structure includes all the fields
described in Section 2.3.1.4.
- If the parameter 'age_limit' is greater than zero, any locally
cached locators for the objective whose remaining lifetime in
milliseconds is less than or equal to 'age_limit' are deleted
first. Thus 'age_limit' = 0 will flush all entries.
- If the parameter 'timeout' is zero, any remaining locally
cached locators for the objective are returned immediately and
no other action is taken. (Thus, a call with 'age_limit' and
'timeout' both equal to zero is pointless.)
- If the parameter 'timeout' is greater than zero, GRASP
discovery is performed, and all results obtained before the
timeout in milliseconds expires are returned. If no results
are obtained, an empty list is returned after the timeout.
That is not an error condition.
- Asynchronous Mechanisms:
o Threaded implementation: This should be called in a separate
thread if asynchronous operation is required.
o Event loop implementation: An additional read/write
'session_nonce' parameter is used. A callback may be used
in the case of a non-zero tiemout.
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2.3.4. Negotiation
* request_negotiate()
- Input parameters:
asa_nonce (integer)
objective (structure)
peer (ASA_locator)
timeout (integer)
- Return parameters:
errorcode (integer)
session_nonce (structure) (if successful)
proffered_objective (structure) (if successful)
reason (string) (if negotiation declined)
- This function opens a negotiation session between two ASAs.
Note that GRASP currently does not support multi-party
negotiation, which would need to be added as an extended
function.
- The 'objective' parameter must include the requested value, and
its loop count should be set to a suitable starting value by
the ASA. If not, the GRASP default will apply.
- Note that a given negotiation session may or may not be a dry-
run negotiation; the two modes must not be mixed in a single
session.
- The 'peer' parameter is the target node; it must be an
'ASA_locator' as returned by discover(). If 'peer' is null,
GRASP discovery is automatically performed first to find a
suitable peer (i.e., any node that supports the objective in
question).
- If the 'errorcode' return parameter is 0, the negotiation has
successfully started. There are then two cases:
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1. The 'session_nonce' parameter is null. In this case the
negotiation has succeeded immediately (the peer has
accepted the request). The returned 'proffered_objective'
contains the value accepted by the peer.
2. The 'session_nonce' parameter is not null. In this case
negotiation must continue. The 'session_nonce' must be
presented in all subsequent negotiation steps. The
returned 'proffered_objective' contains the first value
proffered by the negotiation peer. The contents of this
instance of the objective must be used in the subsequent
negotiation call because it contains the updated loop
count, sent by the negotiation peer. The GRASP code
automatically decrements the loop count by 1 at each step,
and returns an error if it becomes zero.
This function must be followed by calls to 'negotiate_step'
and/or 'negotiate_wait' and/or 'end_negotiate' until the
negotiation ends. 'request_negotiate' may then be called
again to start a new negotiation.
- If the 'errorcode' parameter has the value 1 ('declined'), the
negotiation has been declined by the peer (M_END and O_DECLINE
features of GRASP). The 'reason' string is then available for
information and diagnostic use, but it may be a null string.
For this and any other error code, an exponential backoff is
recommended before any retry.
- Asynchronous Mechanisms:
o Threaded implementation: This should be called in a separate
thread if asynchronous operation is required.
o Event loop implementation: The 'session_nonce' parameter is
used to distinguish multiple simultaneous sessions.
- Use of dry run mode: This must be consistent within a GRASP
session. The state of the 'dry' flag in the initial
request_negotiate() call must be the same in all subsequent
negotiation steps of the same session. The semantics of the
dry run mode are built into the ASA; GRASP merely carries the
flag bit.
- Special note for the ACP infrastructure ASA: It is likely that
this ASA will need to discover and negotiate with its peers in
each of its on-link neighbors. It will therefore need to know
not only the link-local IP address but also the physical
interface and transport port for connecting to each neighbor.
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One implementation approach to this is to include these details
in the 'session_nonce' data structure, which is opaque to
normal ASAs.
* listen_negotiate()
- Input parameters:
asa_nonce (integer)
objective (structure)
- Return parameters:
errorcode (integer)
session_nonce (structure) (if successful)
requested_objective (structure) (if successful)
- This function instructs GRASP to listen for negotiation
requests for the given 'objective'. It also enables discovery
responses for the objective, as mentioned under
register_objective() in Section 2.3.2.
- Asynchronous Mechanisms:
o Threaded implementation: It will block waiting for an
incoming request, so should be called in a separate thread
if asynchronous operation is required. Unless there is an
unexpected failure, this call only returns after an incoming
negotiation request. If the ASA supports multiple
simultaneous transactions, a new thread must be spawned for
each new session.
o Event loop implementation: A 'session_nonce' parameter is
used to distinguish individual sessions. If the ASA
supports multiple simultaneous transactions, a new event
must be inserted in the event loop for each new session.
- This call only returns (threaded model) or triggers (event
loop) after an incoming negotiation request. When this occurs,
'requested_objective' contains the first value requested by the
negotiation peer. The contents of this instance of the