MPLS Working Group Tarek Saad, Ed.
Internet-Draft Rakesh Gandhi, Ed.
Intended status: Standards Track Zafar Ali
Expires: September 11, 2014 Cisco Systems, Inc.
Robert H. Venator
Defense Information Systems Agency
Yuji Kamite
NTT Communications Corporation
March 10, 2014
Reoptimization of Point-to-Multipoint Traffic Engineering
Loosely Routed LSPs
draft-tsaad-mpls-p2mp-loose-path-reopt-01
Abstract
This document defines Resource Reservation Protocol - Traffic
Engineering (RSVP-TE) signaling extensions for reoptimizing loosely
routed Point-to-Multipoint (P2MP) Traffic Engineered (TE) Label
Switched Paths (LSPs) in an Multi-Protocol Label Switching (MPLS) and
Generalized MPLS (GMPLS) networks.
Status of this Memo
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provisions of BCP 78 and BCP 79.
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Copyright Notice
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1. Conventions used in this document . . . . . . . . . . . . 4
3. Signaling Procedure For Loosely Routed P2MP-TE LSP
Reoptimization . . . . . . . . . . . . . . . . . . . . . . . . 5
4. RSVP Signaling Extensions . . . . . . . . . . . . . . . . . . 6
4.1. P2MP-TE Tree Re-evaluation Request Flag . . . . . . . . . 6
4.2. Preferable P2MP-TE Tree Exists Path Error sub-code . . . . 6
5. Compatibility . . . . . . . . . . . . . . . . . . . . . . . . 6
6. Security Considerations . . . . . . . . . . . . . . . . . . . 6
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
7.1. P2MP-TE Tree Re-evaluation Request Flag . . . . . . . . . 7
7.2. Preferable P2MP-TE Tree Exists Path Error sub-code . . . . 7
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 7
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8
9.1. Normative References . . . . . . . . . . . . . . . . . . . 8
9.2. Informative References . . . . . . . . . . . . . . . . . . 8
Author's Addresses . . . . . . . . . . . . . . . . . . . . . . . . 9
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1. Introduction
This document defines Resource Reservation Protocol (RSVP) signaling
extensions for reoptimizing loosely routed Point-to-Multipoint (P2MP)
Multi-Protocol Label Switching (MPLS) and Generalized MPLS (GMPLS)
Traffic Engineered (TE) Label Switched Paths (LSPs) [RFC4875].
A P2MP-TE LSP is comprised of one or more source-to-leaf (S2L)
sub-LSPs. A loosely routed P2MP-TE S2L sub-LSP is defined as one
whose path does not contain the full explicit route identifying each
node along the path to the egress node at the time of its signaling
by the ingress node. Such an S2L sub-LSP is signaled with no
Explicit Route Object (ERO) [RFC3209], or with an ERO that contains
at least one loose hop, or with an ERO that contains an abstract node
that is not a simple abstract node (that is, an abstract node that
identifies more than one node). This is often the case with inter-
domain P2MP-TE LSPs where Path Computation Element (PCE) is not used
[RFC5440].
As per [RFC4875], an ingress node may reoptimize the entire P2MP-TE
LSP by resignaling all its S2L sub-LSP(s) or may reoptimize
individual S2L sub-LSP(s) i.e. individual destination(s).
[RFC4736] defines RSVP signaling extensions for reoptimizing loosely
routed P2P TE LSP(s). Specifically, an ingress node sends a "Path
Re-evaluation Request" to a border node by setting a flag (0x20) in
SESSION_ATTRIBUTES object in the Path message. A border node sends a
PathErr code 25 (notify error defined in [RFC3209]) with sub-code 6
to indicate "Preferable Path Exists" to the ingress node which may be
solicited or unsolicited. The ingress node upon receiving this
PathErr either solicited or unsolicited initiates reoptimization of
the LSP.
[RFC4736] does not define signaling extensions specific for
reoptimizing entire P2MP-TE LSP tree. Mechanisms defined in
[RFC4736] can be used for signaling the reoptimization of individual
S2L sub- LSP(s). However, to use [RFC4736] mechanisms for
reoptimizing an entire P2MP-TE LSP tree, an ingress node needs to
send the query on all (typically 100s of) S2L sub-LSPs and a border
node needs to notify PathErrs for all S2L sub-LSPs. Such requirement
can lead to the following issues.
- A border node has to accumulate the received queries on all S2L
sub-LSPs (using a wait timer) and interpret them as a reoptimization
request for the P2MP-TE LSP tree. A border node may prematurely
notify "Preferable Path Exists" for a sub-set of S2L sub-LSPs.
- When the ingress node gradually receives unsolicited PathErr
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notifications for individual S2L sub-LSPs, it may prematurely start
reoptimizing a sub-set of S2L sub-LSPs. However, as mentioned in
[RFC4875] Section 14.2, such reoptimization procedure may result in
data duplication that can be avoided if the entire P2MP-TE LSP tree
is reoptimized, especially if the ingress node eventually receives
PathErr notifications for all S2L sub-LSPs of the P2MP-TE LSP tree.
- The ingress node may have to heuristically determine when to
perform entire P2MP-TE LSP tree reoptimization versus per S2L sub-LSP
reoptimization, for example, to delay reoptimization long enough time
to accumulate all PathErr(s) to be received. Such requirements may
produce undesired results due to timing related issues which can be
easily avoided by the RSVP signaling messages defined in this
document.
This document defines RSVP signaling extensions to query and notify a
preferable path for reoptimizing loosely routed P2MP-TE LSP tree.
2. Terminology
ABR: Area Border Router.
ERO: Explicit Route Object.
TE LSP: Traffic Engineering Label Switched Path.
TE LSP ingress: head/source of the TE LSP.
TE LSP egress: tail/destination of the TE LSP.
S2L: Source-to-leaf.
Interior Gateway Protocol Area (IGP Area): OSPF Area or IS-IS level.
Inter-area TE LSP: A TE LSP whose path transits across at least two
different IGP areas.
Inter-AS MPLS TE LSP: A TE LSP whose path transits across at least
two different Autonomous Systems (ASes) or sub-ASes (BGP
confederations).
2.1. Conventions used in this document
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 [RFC2119]. The reader
is assumed to be familiar with the terminology in [RFC4875] and
[RFC4736].
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3. Signaling Procedure For Loosely Routed P2MP-TE LSP Reoptimization
As per [RFC4875], an ingress node may prefer to reoptimize the entire
P2MP-TE LSP by resignaling all its S2L sub-LSP(s) (Section 14.1,
"Make-before- Break") or reoptimize individual S2L sub-LSP(s) i.e.
individual destination(s) (Section 14.2 "Sub-Group-Based Re-
Optimization").
An ingress node uses procedures defined in [RFC4736] to individually
reoptimize the S2L sub-LSP(s) i.e. destination(s) of a P2MP-TE LSP.
To reoptimize an entire P2MP-TE LSP tree, in order to query border
nodes to check if a preferable P2MP-TE LSP tree exists, an ingress
node sends a Path message with "P2MP-TE Tree Re-evaluation Request"
defined in this document. An ingress node may select one or more S2L
sub-LSP of the P2MP-TE LSP tree transiting through the border node to
send the query to that border node.
A border node receiving the "P2MP-TE Tree Re-evaluation Request"
checks for a preferable P2MP-TE LSP tree by re-evaluating loosely
expanded paths for all S2L sub-LSP(s) of the P2MP-TE LSP. If a
preferable P2MP-TE LSP tree is found, the border node immediately
sends an RSVP PathErr to the ingress node with Error code 25 (Notify
defined in [RFC3209] and Error sub-code defined in this document
"Preferable P2MP-TE Tree Exists". At this point, the border node
does not propagate this bit in subsequent RSVP Path messages sent
downstream for the re-evaluated P2MP-TE LSP. The sending of an RSVP
PathErr Notify message "Preferable P2MP-TE Tree Exists" to the
ingress node will notify the ingress node of the existence of a
preferable P2MP-TE LSP tree.
If no preferable path for P2MP-TE LSP tree can be found, the
recommended mode is for the border node to relay the request
downstream by setting the "P2MP-TE Tree Re-evaluation Request" bit in
the LSP_ATTRIBUTES TLV of RSVP Path message.
A border node may send "Preferable P2MP-TE Tree Exists" with PathErr
code 25 to the ingress node to notify an existence of a preferred
path for the P2MP-TE LSP tree with an unsolicited PathErr message.
The border node may select one or more S2L sub-LSP(s) of the P2MP-TE
LSP tree to send this PathErr message to the ingress node.
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4. RSVP Signaling Extensions
4.1. P2MP-TE Tree Re-evaluation Request Flag
In order to query border nodes to check if a preferable P2MP-TE LSP
tree exists, a new flag is defined in Attributes Flags TLV of the
LSP_ATTRIBUTES object [RFC5420] as follows:
Bit Number (to be assigned by IANA): P2MP-TE Tree Re-evaluation
Request flag
The "P2MP-TE Tree Re-evaluation Request" flag is meaningful in a Path
message of a P2MP-TE S2L sub-LSP and is inserted by the ingress node.
4.2. Preferable P2MP-TE Tree Exists Path Error sub-code
In order to indicate to an ingress node that a preferable P2MP-TE LSP
tree is available, following new sub-code for PathErr code 25 (Notify
Error) [RFC3209] is defined:
Sub-code (to be assigned by IANA): Preferable P2MP-TE Tree Exists
sub-code
When a preferable path for P2MP-TE LSP tree is found, the border node
sends a solicited or unsolicited "Preferable P2MP-TE Tree Exists"
PathErr notification to the ingress node of the P2MP-TE LSP.
5. Compatibility
The LSP_ATTRIBUTES TLV has been defined in [RFC5420] with class
numbers in the form 11bbbbbb, which ensures compatibility with
non-supporting nodes. Per [RFC2205], nodes not supporting this
extension will ignore the new flag defined in this document but
forward it without modification.
6. Security Considerations
This document does not introduce any additional security issues above
those identified in [RFC3209] and [RFC4875].
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7. IANA Considerations
IANA maintains a name space for RSVP-TE TE parameters "Resource
Reservation Protocol-Traffic Engineering (RSVP-TE) Parameters". From
the registries in this name space "Attribute Flags" allocation of new
flag is requested (Section 4.1).
IANA also maintains a name space for RSVP protocol parameters
"Resource Reservation Protocol (RSVP) Parameters". From the sub-
registry "Sub-Codes - 25 Notify Error" in registry "Error Codes and
Globally-Defined Error Value Sub-Codes" allocation of a new error
code is requested (Section 4.2).
7.1. P2MP-TE Tree Re-evaluation Request Flag
The following new flag is defined for the Attributes Flags TLV in the
LSP_ATTRIBUTES object [RFC5420]. The numeric values are to be
assigned by IANA.
o P2MP-TE Tree Re-evaluation Request Flag:
- Bit Number: To be assigned by IANA.
- Attribute flag carried in Path message: Yes
- Attribute flag carried in Resv message: No
7.2. Preferable P2MP-TE Tree Exists Path Error sub-code
As defined in [RFC3209], the Error Code 25 in the ERROR SPEC object
corresponds to a Notify Error PathErr. This document adds a new sub-
code as follows for this PathErr:
o Preferable P2MP-TE Tree Exists sub-code:
- Sub-code for Notify PathErr code 25. To be assigned by IANA.
8. Acknowledgments
TBA.
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9. References
9.1. Normative References
[RFC2205] Braden, R., Ed., Zhang, L., Berson, S., Herzog, S., and S.
Jamin, "Resource ReSerVation Protocol (RSVP) -- Version 1
Functional Specification", RFC 2205, September 1997.
[RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
Tunnels", RFC 3209, December 2001.
[RFC4875] Aggarwal, R., Papadimitriou, D., and S. Yasukawa,
"Extensions to Resource Reservation Protocol Traffic
Engineering (RSVP-TE) for Point-to-Multipoint TE Label
Switched Paths (LSPs)", RFC 4875, May 2007.
[RFC5420] Farrel, A., Papadimitriou, D., Vasseur, JP., and A.
Ayyangarps, "Encoding of Attributes for MPLS LSP
Establishment Using Resource Reservation Protocol Traffic
Engineering (RSVP-TE)", RFC 5420, February 2009.
9.2. Informative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4736] Vasseur, JP., Ikejiri, Y. and Zhang, R, "Reoptimization of
Multiprotocol Label Switching (MPLS) Traffic Engineering
(TE) Loosely Routed Label Switched Path (LSP)", RFC 4736,
November 2006.
[RFC5440] Vasseur, JP., Ed., and JL. Le Roux, Ed., "Path Computation
Element (PCE) Communication Protocol (PCEP)", RFC 5440,
March 2009.
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Author's Addresses
Tarek Saad (editor)
Cisco Systems
Email: tsaad@cisco.com
Rakesh Gandhi (editor)
Cisco Systems
Email: rgandhi@cisco.com
Zafar Ali
Cisco Systems
Email: zali@cisco.com
Robert H. Venator
Defense Information Systems Agency
Email: robert.h.venator.civ@mail.mil
Yuji Kamite
NTT Communications Corporation
Email: y.kamite@ntt.com
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