Extensions to the Path Computation Element Communication Protocol (PCEP) for Point-to-Multipoint Traffic Engineering Label Switched Paths :: RFC6006
Internet Engineering Task Force (IETF) Q. Zhao, Ed.
Request for Comments: 6006 Huawei Technology
Category: Standards Track D. King, Ed.
ISSN: 2070-1721 Old Dog Consulting
F. Verhaeghe
Thales Communication France
T. Takeda
NTT Corporation
Z. Ali
Cisco Systems, Inc.
J. Meuric
France Telecom
September 2010
Extensions to
the Path Computation Element Communication Protocol (PCEP)
for Point-to-Multipoint Traffic Engineering Label Switched Paths
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.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc6006.
Zhao, et al. Standards Track [Page 1]
RFC 6006 Extensions to PCEP for P2MP TE LSPs September 2010
Copyright Notice
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Table of Contents
1. Introduction ....................................................3
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 ..............................7
3.2. Efficient Presentation of P2MP LSPs ........................7
3.3. P2MP Path Computation Request/Reply Message Extensions .....8
3.3.1. The Extension of the RP Object ......................8
3.3.2. The New P2MP END-POINTS Object ......................9
3.4. Request Message Format ....................................12
3.5. Reply Message Format ......................................12
3.6. P2MP Objective Functions and Metric Types .................13
3.6.1. New Objective Functions ............................13
3.6.2. New Metric Object Types ............................14
3.7. Non-Support of P2MP Path Computation ......................14
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3.8. Non-Support by Back-Level PCE Implementations .............15
3.9. P2MP TE Path Reoptimization Request .......................15
3.10. Adding and Pruning Leaves to/from the P2MP Tree ..........16
3.11. Discovering Branch Nodes .................................19
3.11.1. Branch Node Object ................................19
3.12. Synchronization of P2MP TE Path Computation Requests .....19
3.13. Request and Response Fragmentation .......................20
3.13.1. Request Fragmentation Procedure ...................21
3.13.2. Response Fragmentation Procedure ..................21
3.13.3. Fragmentation Examples ............................21
3.14. UNREACH-DESTINATION Object ...............................22
3.15. P2MP PCEP-ERROR Objects and Types ........................23
3.16. PCEP NO-PATH Indicator ...................................24
4. Manageability Considerations ...................................25
4.1. Control of Function and Policy ............................25
4.2. Information and Data Models ...............................25
4.3. Liveness Detection and Monitoring .........................25
4.4. Verifying Correct Operation ...............................25
4.5. Requirements for Other Protocols and Functional
Components ................................................26
4.6. Impact on Network Operation ...............................26
5. Security Considerations ........................................26
6. IANA Considerations ............................................27
6.1. PCEP TLV Type Indicators ..................................27
6.2. Request Parameter Bit Flags ...............................27
6.3. Objective Functions .......................................27
6.4. Metric Object Types .......................................27
6.5. PCEP Objects ..............................................28
6.6. PCEP-ERROR Objects and Types ..............................29
6.7. PCEP NO-PATH Indicator ....................................30
6.8. SVEC Object Flag ..........................................30
6.9. OSPF PCE Capability Flag ..................................30
7. Acknowledgements ...............................................30
8. References .....................................................30
8.1. Normative References ......................................30
8.2. Informative References ....................................32
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.
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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.
1.1. Terminology
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].
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1.2. Requirements Language
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 [RFC2119].
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
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.
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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
[RFC4970] 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
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 1: SERO
2-15: Unassigned
Reference RFC 6006
Object-Class Value 30
Name SRRO
Object-Type 1: SRRO
2-15: Unassigned
Reference RFC 6006
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
The PCReq message is encoded as follows using RBNF as defined in
[RFC5511].
Below is the message format for the request message:
::=
where:
::=
RFC, FYI, BCP
