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draft-ietf-pce-rfc6006bis-04.txt
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draft-ietf-pce-rfc6006bis-04.txt
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PCE Working Group Q. Zhao
Internet-Draft D. Dhody, Ed.
Intended status: Standards Track R. Palleti
Obsoletes: 6006 (if approved) Huawei Technology
Expires: March 30, 2018 D. King
Old Dog Consulting
September 26, 2017
Extensions to
the Path Computation Element Communication Protocol (PCEP)
for Point-to-Multipoint Traffic Engineering Label Switched Paths
draft-ietf-pce-rfc6006bis-04
Abstract
Point-to-point Multiprotocol Label Switching (MPLS) and Generalized
MPLS (GMPLS) Traffic Engineering Label Switched Paths (TE LSPs) may
be established using signaling techniques, but their paths may first
need to be determined. The Path Computation Element (PCE) has been
identified as an appropriate technology for the determination of the
paths of point-to-multipoint (P2MP) TE LSPs.
This document describes extensions to the PCE communication Protocol
(PCEP) to handle requests and responses for the computation of paths
for P2MP TE LSPs.
This document obsoletes RFC 6006.
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 http://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 March 30, 2018.
Palleti. Expires March 2018 [Page 1]
draft-ietf-pce-rfc6006bis September 2017
Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://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.
This document may contain material from IETF Documents or IETF
Contributions published or made publicly available before November
10, 2008. The person(s) controlling the copyright in some of this
material may not have granted the IETF Trust the right to allow
modifications of such material outside the IETF Standards Process.
Without obtaining an adequate license from the person(s) controlling
the copyright in such materials, this document may not be modified
outside the IETF Standards Process, and derivative works of it may
not be created outside the IETF Standards Process, except to format
it for publication as an RFC or to translate it into languages other
than English.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
1.2. Requirements Language . . . . . . . . . . . . . . . . . . 5
2. PCC-PCE Communication Requirements . . . . . . . . . . . . . . 5
3. Protocol Procedures and Extensions . . . . . . . . . . . . . . 6
3.1. P2MP Capability Advertisement . . . . . . . . . . . . . . 6
3.1.1. P2MP Computation TLV in the Existing PCE Discovery
Protocol . . . . . . . . . . . . . . . . . . . . . . . 6
3.1.2. Open Message Extension . . . . . . . . . . . . . . . . 8
3.2. Efficient Presentation of P2MP LSPs . . . . . . . . . . . 8
3.3. P2MP Path Computation Request/Reply Message Extensions . . 9
3.3.1. The Extension of the RP Object . . . . . . . . . . . . 9
3.3.2. The New P2MP END-POINTS Object . . . . . . . . . . . . 10
3.4. Request Message Format . . . . . . . . . . . . . . . . . . 13
3.5. Reply Message Format . . . . . . . . . . . . . . . . . . . 14
3.6. P2MP Objective Functions and Metric Types . . . . . . . . 15
3.6.1. New Objective Functions . . . . . . . . . . . . . . . 15
3.6.2. New Metric Object Types . . . . . . . . . . . . . . . 16
3.7. Non-Support of P2MP Path Computation . . . . . . . . . . . 16
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3.8. Non-Support by Back-Level PCE Implementations . . . . . . 18
3.9. P2MP TE Path Reoptimization Request . . . . . . . . . . . 18
3.10. Adding and Pruning Leaves to/from the P2MP Tree . . . . . 19
3.11. Discovering Branch Nodes . . . . . . . . . . . . . . . . 22
3.11.1. Branch Node Object . . . . . . . . . . . . . . . . . 22
3.12. Synchronization of P2MP TE Path Computation Requests . . 22
3.13. Request and Response Fragmentation . . . . . . . . . . . 23
3.13.1. Request Fragmentation Procedure . . . . . . . . . . . 24
3.13.2. Response Fragmentation Procedure . . . . . . . . . . 24
3.13.3. Fragmentation Examples . . . . . . . . . . . . . . . 24
3.14. UNREACH-DESTINATION Object . . . . . . . . . . . . . . . 25
3.15. P2MP PCEP-ERROR Objects and Types . . . . . . . . . . . . 26
3.16. PCEP NO-PATH Indicator . . . . . . . . . . . . . . . . . 27
4. Manageability Considerations . . . . . . . . . . . . . . . . . 28
4.1. Control of Function and Policy . . . . . . . . . . . . . . 28
4.2. Information and Data Models . . . . . . . . . . . . . . . 28
4.3. Liveness Detection and Monitoring . . . . . . . . . . . . 28
4.4. Verifying Correct Operation . . . . . . . . . . . . . . . 29
4.5. Requirements for Other Protocols and Functional
Components . . . . . . . . . . . . . . . . . . . . . . . . 30
4.6. Impact on Network Operation . . . . . . . . . . . . . . . 30
5. Security Considerations . . . . . . . . . . . . . . . . . . . 30
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 31
6.1. PCEP TLV Type Indicators . . . . . . . . . . . . . . . . . 31
6.2. Request Parameter Bit Flags . . . . . . . . . . . . . . . 31
6.3. Objective Functions . . . . . . . . . . . . . . . . . . . 31
6.4. Metric Object Types . . . . . . . . . . . . . . . . . . . 32
6.5. PCEP Objects . . . . . . . . . . . . . . . . . . . . . . . 32
6.6. PCEP-ERROR Objects and Types . . . . . . . . . . . . . . . 33
6.7. PCEP NO-PATH Indicator . . . . . . . . . . . . . . . . . . 34
6.8. SVEC Object Flag . . . . . . . . . . . . . . . . . . . . . 34
6.9. OSPF PCE Capability Flag . . . . . . . . . . . . . . . . . 35
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 35
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 37
8.1. Normative References . . . . . . . . . . . . . . . . . . . 37
8.2. Informative References . . . . . . . . . . . . . . . . . . 38
Appendix A. Summary of the all Changes from RFC 6006 . . . . . . . 40
Appendix A.1 RBNF Changes from RFC 6006 . . . . . . . . . . . . . 40
Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 43
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1. Introduction
The Path Computation Element (PCE) defined in [RFC4655] is an entity
that is capable of computing a network path or route based on a
network graph, and applying computational constraints. A Path
Computation Client (PCC) may make requests to a PCE for paths to be
computed.
[RFC4875] describes how to set up point-to-multipoint (P2MP) Traffic
Engineering Label Switched Paths (TE LSPs) for use in Multiprotocol
Label Switching (MPLS) and Generalized MPLS (GMPLS) networks.
The PCE has been identified as a suitable application for the
computation of paths for P2MP TE LSPs [RFC5671].
The PCE communication Protocol (PCEP) is designed as a communication
protocol between PCCs and PCEs for point-to-point (P2P) path
computations and is defined in [RFC5440]. However, that
specification does not provide a mechanism to request path
computation of P2MP TE LSPs.
A P2MP LSP is comprised of multiple source-to-leaf (S2L) sub-LSPs.
These S2L sub-LSPs are set up between ingress and egress Label
Switching Routers (LSRs) and are appropriately overlaid to construct
a P2MP TE LSP. During path computation, the P2MP TE LSP may be
determined as a set of S2L sub-LSPs that are computed separately and
combined to give the path of the P2MP LSP, or the entire P2MP TE LSP
may be determined as a P2MP tree in a single computation.
This document relies on the mechanisms of PCEP to request path
computation for P2MP TE LSPs. One path computation request message
from a PCC may request the computation of the whole P2MP TE LSP, or
the request may be limited to a sub-set of the S2L sub-LSPs. In the
extreme case, the PCC may request the S2L sub-LSPs to be computed
individually with it being the PCC's responsibility to decide whether
to signal individual S2L sub-LSPs or combine the computation results
to signal the entire P2MP TE LSP. Hence the PCC may use one path
computation request message or may split the request across multiple
path computation messages.
This document obsoletes [RFC6006] and incorporates all outstanding
Errata:
o Erratum with IDs: 3819, 3830, 3836, 4867, 4868 and 4956.
All changes from [RFC6006] are listed in Appendix A.
1.1. Terminology
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Terminology used in this document:
TE LSP: Traffic Engineering Label Switched Path.
LSR: Label Switching Router.
OF: Objective Function: A set of one or more optimization criteria
used for the computation of a single path (e.g., path cost
minimization), or for the synchronized computation of a set of
paths (e.g., aggregate bandwidth consumption minimization).
P2MP: Point-to-Multipoint.
P2P: Point-to-Point.
This document also uses the terminology defined in [RFC4655],
[RFC4875], and [RFC5440].
1.2. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
2. PCC-PCE Communication Requirements
This section summarizes the PCC-PCE communication requirements for
P2MP MPLS-TE LSPs described in [RFC5862]. The numbering system
corresponds to the requirement numbers used in [RFC5862].
1. The PCC MUST be able to specify that the request is a P2MP path
computation request.
2. The PCC MUST be able to specify that objective functions are to
be applied to the P2MP path computation request.
3. The PCE MUST have the capability to reject a P2MP path request
and indicate non-support of P2MP path computation.
4. The PCE MUST provide an indication of non-support of P2MP path
computation by back-level PCE implementations.
5. A P2MP path computation request MUST be able to list multiple
destinations.
6. A P2MP path computation response MUST be able to carry the path
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of a P2MP LSP.
7. By default, the path returned by the PCE SHOULD use the
compressed format.
8. It MUST be possible for a single P2MP path computation request or
response to be conveyed by a sequence of messages.
9. It MUST NOT be possible for a single P2MP path computation
request to specify a set of different constraints, traffic
parameters, or quality-of-service requirements for different
destinations of a P2MP LSP.
10. P2MP path modification and P2MP path diversity MUST be supported.
11. It MUST be possible to reoptimize existing P2MP TE LSPs.
12. It MUST be possible to add and remove P2MP destinations from
existing paths.
13. It MUST be possible to specify a list of applicable branch nodes
to use when computing the P2MP path.
14. It MUST be possible for a PCC to discover P2MP path computation
capability.
15. The PCC MUST be able to request diverse paths when requesting a
P2MP path.
3. Protocol Procedures and Extensions
The following section describes the protocol extensions required to
satisfy the requirements specified in Section 2 ("PCC-PCE
Communication Requirements") of this document.
3.1. P2MP Capability Advertisement
3.1.1. P2MP Computation TLV in the Existing PCE Discovery Protocol
[RFC5088] defines a PCE Discovery (PCED) TLV carried in an OSPF
Router Information Link State Advertisement (LSA) defined in
[RFC7770] to facilitate PCE discovery using OSPF. [RFC5088]
specifies that no new sub-TLVs may be added to the PCED TLV. This
document defines a new flag in the OSPF PCE Capability Flags to
indicate the capability of P2MP computation.
Similarly, [RFC5089] defines the PCED sub-TLV for use in PCE
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Discovery using IS-IS. This document will use the same flag
requested for the OSPF PCE Capability Flags sub-TLV to allow IS-IS to
indicate the capability of P2MP computation.
The IANA assignment for a shared OSPF and IS-IS P2MP Capability Flag
is documented in Section 6.9 ("OSPF PCE Capability Flag") of this
document.
PCEs wishing to advertise that they support P2MP path computation
would set the bit (10) accordingly. PCCs that do not understand this
bit will ignore it (per [RFC5088] and [RFC5089]). PCEs that do not
support P2MP will leave the bit clear (per the default behavior
defined in [RFC5088] and [RFC5089]).
PCEs that set the bit to indicate support of P2MP path computation
MUST follow the procedures in Section 3.3.2 ("The New P2MP END-POINTS
Object") to further qualify the level of support.
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3.1.2. Open Message Extension
Based on the Capabilities Exchange requirement described in
[RFC5862], if a PCE does not advertise its P2MP capability during
discovery, PCEP should be used to allow a PCC to discover, during the
Open Message Exchange, which PCEs are capable of supporting P2MP path
computation.
To satisfy this requirement, we extend the PCEP OPEN object by
defining a new optional TLV to indicate the PCE's capability to
perform P2MP path computations.
IANA has allocated value 6 from the "PCEP TLV Type Indicators" sub-
registry, as documented in Section 6.1 ("PCEP TLV Type Indicators").
The description is "P2MP capable", and the length value is 2 bytes.
The value field is set to default value 0.
The inclusion of this TLV in an OPEN object indicates that the sender
can perform P2MP path computations.
The capability TLV is meaningful only for a PCE, so it will typically
appear only in one of the two Open messages during PCE session
establishment. However, in case of PCE cooperation (e.g.,
inter-domain), when a PCE behaving as a PCC initiates a PCE session
it SHOULD also indicate its path computation capabilities.
3.2. Efficient Presentation of P2MP LSPs
When specifying additional leaves, or optimizing existing P2MP TE
LSPs as specified in [RFC5862], it may be necessary to pass existing
P2MP LSP route information between the PCC and PCE in the request and
reply messages. In each of these scenarios, we need new path objects
for efficiently passing the existing P2MP LSP between the PCE and
PCC.
We specify the use of the Resource Reservation Protocol Traffic
Engineering (RSVP-TE) extensions Explicit Route Object (ERO) to
encode the explicit route of a TE LSP through the network. PCEP ERO
sub-object types correspond to RSVP-TE ERO sub-object types. The
format and content of the ERO object are defined in [RFC3209] and
[RFC3473].
The Secondary Explicit Route Object (SERO) is used to specify the
explicit route of a S2L sub-LSP. The path of each subsequent S2L
sub-LSP is encoded in a P2MP_SECONDARY_EXPLICIT_ROUTE object SERO.
The format of the SERO is the same as an ERO defined in [RFC3209] and
[RFC3473].
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The Secondary Record Route Object (SRRO) is used to record the
explicit route of the S2L sub-LSP. The class of the P2MP SRRO is the
same as the SRRO defined in [RFC4873].
The SERO and SRRO are used to report the route of an existing TE LSP
for which a reoptimization is desired. The format and content of the
SERO and SRRO are defined in [RFC4875].
A new PCEP object class and type are requested for SERO and SRRO.
Object-Class Value 29
Name SERO
Object-Type 0: Reserved
1: SERO
2-15: Unassigned
Reference [This I-D]
Object-Class Value 30
Name SRRO
Object-Type 0: Reserved
1: SRRO
2-15: Unassigned
Reference [This I-D]
The IANA assignment is documented in Section 6.5 ("PCEP Objects").
Since the explicit path is available for immediate signaling by the
MPLS or GMPLS control plane, the meanings of all of the sub-objects
and fields in this object are identical to those defined for the ERO.
3.3. P2MP Path Computation Request/Reply Message Extensions
This document extends the existing P2P RP (Request Parameters) object
so that a PCC can signal a P2MP path computation request to the PCE
receiving the PCEP request. The END-POINTS object is also extended
to improve the efficiency of the message exchange between PCC and PCE
in the case of P2MP path computation.
3.3.1. The Extension of the RP Object
The PCE path computation request and reply messages will need the
following additional parameters to indicate to the receiving PCE that
the request and reply messages have been fragmented across multiple
messages, that they have been requested for a P2MP path, and whether
the route is represented in the compressed or uncompressed format.
This document adds the following flags to the RP Object:
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The F-bit is added to the flag bits of the RP object to indicate to
the receiver that the request is part of a fragmented request, or is
not a fragmented request.
o F (RP fragmentation bit - 1 bit):
0: This indicates that the RP is not fragmented or it is the last
piece of the fragmented RP.
1: This indicates that the RP is fragmented and this is not the
last piece of the fragmented RP. The receiver needs to wait
for additional fragments until it receives an RP with the same
RP-ID and with the F-bit set to 0.
The N-bit is added in the flag bits field of the RP object to signal
the receiver of the message that the request/reply is for P2MP or is
not for P2MP.
o N (P2MP bit - 1 bit):
0: This indicates that this is not a PCReq or PCRep message for
P2MP.
1: This indicates that this is a PCReq or PCRep message for P2MP.
The E-bit is added in the flag bits field of the RP object to signal
the receiver of the message that the route is in the compressed
format or is not in the compressed format. By default, the path
returned by the PCE SHOULD use the compressed format.
o E (ERO-compression bit - 1 bit):
0: This indicates that the route is not in the compressed format.
1: This indicates that the route is in the compressed format.
The IANA assignment is documented in Section 6.2 ("Request Parameter
Bit Flags") of this document.
3.3.2. The New P2MP END-POINTS Object
The END-POINTS object is used in a PCReq message to specify the
source IP address and the destination IP address of the path for
which a path computation is requested. To represent the end points
for a P2MP path efficiently, we define two new types of END-POINTS
objects for the P2MP path:
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o Old leaves whose path can be modified/reoptimized;
o Old leaves whose path must be left unchanged.
With the new END-POINTS object, the PCE path computation request
message is expanded in a way that allows a single request message to
list multiple destinations.
In total, there are now 4 possible types of leaves in a P2MP request:
o New leaves to add (leaf type = 1)
o Old leaves to remove (leaf type = 2)
o Old leaves whose path can be modified/reoptimized (leaf type = 3)
o Old leaves whose path must be left unchanged (leaf type = 4)
A given END-POINTS object gathers the leaves of a given type. The
type of leaf in a given END-POINTS object is identified by the END-
POINTS object leaf type field.
Using the new END-POINTS object, the END-POINTS portion of a request
message for the multiple destinations can be reduced by up to 50% for
a P2MP path where a single source address has a very large number of
destinations.
Note that a P2MP path computation request can mix the different types
of leaves by including several END-POINTS objects per RP object as
shown in the PCReq Routing Backus-Naur Form (RBNF) [RFC5511] format
in Section 3.4 ("Request Message Format").
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The format of the new END-POINTS object body for IPv4 (Object-Type 3)
is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Leaf type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source IPv4 address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Destination IPv4 address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ... ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Destination IPv4 address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1. The New P2MP END-POINTS Object Body Format for IPv4
The format of the END-POINTS object body for IPv6 (Object-Type 4) is
as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Leaf type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Source IPv6 address (16 bytes) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Destination IPv6 address (16 bytes) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ... ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Destination IPv6 address (16 bytes) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2. The New P2MP END-POINTS Object Body Format for IPv6
The END-POINTS object body has a variable length. These are
multiples of 4 bytes for IPv4, and multiples of 16 bytes, plus 4
bytes, for IPv6.
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3.4. Request Message Format
As per [RFC5440], a Path Computation Request message (also referred
to as a PCReq message) is a PCEP message sent by a PCC to a PCE to
request a path computation. A PCReq message may carry more than one
path computation request.
As per [RFC5541], the OF object MAY be carried within a PCReq
message. If an objective function is to be applied to a set of
synchronized path computation requests, the OF object MUST be carried
just after the corresponding SVEC (Synchronization VECtor) object and
MUST NOT be repeated for each elementary request.
The PCReq message is encoded as follows using RBNF as defined in
[RFC5511].
Below is the message format for the request message:
<PCReq Message>::= <Common Header>
[<svec-list>]
<request-list>
where:
<svec-list>::=<SVEC>
[<OF>]
[<metric-list>]
[<svec-list>]
<request-list>::=<request>[<request-list>]
<request>::= <RP>
<end-point-rro-pair-list>
[<OF>]
[<LSPA>]
[<BANDWIDTH>]
[<metric-list>]
[<IRO>|<BNC>]
[<LOAD-BALANCING>]
where:
<end-point-rro-pair-list>::=
<END-POINTS>[<RRO-List>[<BANDWIDTH>]]
[<end-point-rro-pair-list>]
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<RRO-List>::=(<RRO>|<SRRO>)[<RRO-List>]
<metric-list>::=<METRIC>[<metric-list>]
Figure 3. The Message Format for the Request Message
Note that we preserve compatibility with the [RFC5440] definition of
<request>. At least one instance of <endpoints> MUST be present in
this message.
We have documented the IANA assignment of additional END-POINTS
Object-Types in Section 6.5 ("PCEP Objects") of this document.
3.5. Reply Message Format
The PCEP Path Computation Reply message (also referred to as a PCRep
message) is a PCEP message sent by a PCE to a requesting PCC in
response to a previously received PCReq message. PCEP supports the
bundling of multiple replies to a set of path computation requests
within a single PCRep message.
The PCRep message is encoded as follows using RBNF as defined in
[RFC5511].
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Below is the message format for the reply message:
<PCRep Message>::= <Common Header>
<response-list>
where:
<response-list>::=<response>[<response-list>]
<response>::=<RP>
[<end-point-path-pair-list>]
[<NO-PATH>]
[<UNREACH-DESTINATION>]
[<attribute-list>]
<end-point-path-pair-list>::=
[<END-POINTS>]<path>
[<end-point-path-pair-list>]
<path> ::= (<ERO>|<SERO>) [<path>]
where:
<attribute-list>::=[<OF>]
[<LSPA>]
[<BANDWIDTH>]
[<metric-list>]
[<IRO>]
Figure 4. The Message Format for the Reply Message
The optional END-POINTS object in the reply message is used to
specify which paths are removed, changed, not changed, or added for
the request. The path is only needed for the end points that are
added or changed.
If the E-bit (ERO-Compress bit) was set to 1 in the request, then the
path will be formed by an ERO followed by a list of SEROs.
Note that we preserve compatibility with the [RFC5440] definition of
<response> and the optional <end-point-path-pair-list> and <path>.
3.6. P2MP Objective Functions and Metric Types
3.6.1. New Objective Functions
Six objective functions have been defined in [RFC5541] for P2P path
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computation.
This document defines two additional objective functions -- namely,
SPT (Shortest Path Tree) and MCT (Minimum Cost Tree) that apply to
P2MP path computation. Hence two new objective function codes have
to be defined.
The description of the two new objective functions is as follows.
Objective Function Code: 7
Name: Shortest Path Tree (SPT)
Description: Minimize the maximum source-to-leaf cost with respect
to a specific metric or to the TE metric used as the default
metric when the metric is not specified (e.g., TE or IGP metric).
Objective Function Code: 8
Name: Minimum Cost Tree (MCT)
Description: Minimize the total cost of the tree, that is the sum
of the costs of tree links, with respect to a specific metric or
to the TE metric used as the default metric when the metric is not
specified.
Processing these two new objective functions is subject to the rules
defined in [RFC5541].
3.6.2. New Metric Object Types
There are three types defined for the <METRIC> object in [RFC5440] --
namely, the IGP metric, the TE metric, and the hop count metric. This
document defines three additional types for the <METRIC> object: the
P2MP IGP metric, the P2MP TE metric, and the P2MP hop count metric.
They encode the sum of the metrics of all links of the tree. We
propose the following values for these new metric types:
o P2MP IGP metric: T=8
o P2MP TE metric: T=9
o P2MP hop count metric: T=10
3.7. Non-Support of P2MP Path Computation
o If a PCE receives a P2MP path request and it understands the P2MP
flag in the RP object, but the PCE is not capable of P2MP
computation, the PCE MUST send a PCErr message with a PCEP-ERROR
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object and corresponding Error-Value. The request MUST then be
cancelled at the PCC. New Error-Types and Error-Values are
requested in Section 6 ("IANA Considerations") of this document.
o If the PCE does not understand the P2MP flag in the RP object,
then the PCE MUST send a PCErr message with Error-value=2
(capability not supported).
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3.8. Non-Support by Back-Level PCE Implementations
If a PCE receives a P2MP request and the PCE does not understand the
P2MP flag in the RP object, and therefore the PCEP P2MP extensions,
then the PCE SHOULD reject the request.
3.9. P2MP TE Path Reoptimization Request
A reoptimization request for a P2MP TE path is specified by the use
of the R-bit within the RP object as defined in [RFC5440] and is
similar to the reoptimization request for a P2P TE path. The only
difference is that the PCC MUST insert the list of RROs and SRROs
after each type of END-POINTS in the PCReq message, as described in
the "Request Message Format" section (Section 3.4) of this document.
An example of a reoptimization request and subsequent PCReq message
is described below:
Common Header
RP with P2MP flag/R-bit set
END-POINTS for leaf type 3
RRO list
OF (optional)
Figure 5. PCReq Message Example 1 for Optimization
In this example, we request reoptimization of the path to all leaves
without adding or pruning leaves. The reoptimization request would
use an END-POINT type 3. The RRO list would represent the P2MP LSP
before the optimization, and the modifiable path leaves would be
indicated in the END-POINTS object.
It is also possible to specify distinct leaves whose path cannot be
modified. An example of the PCReq message in this scenario would be:
Common Header
RP with P2MP flag/R-bit set
END-POINTS for leaf type 3
RRO list
END-POINTS for leaf type 4
RRO list
OF (optional)
Figure 6. PCReq Message Example 2 for Optimization