MPLS Working Group Tarek Saad
Internet-Draft Rakesh Gandhi
Intended status: Informational Zafar Ali
Expires: July 28, 2014 Cisco Systems, Inc.
Robert H. Venator
Defense Information Systems Agency
Yuji Kamite
NTT Communications Corporation
January 24, 2014
Reoptimization of Point-to-Multipoint Traffic Engineering
Loosely Routed LSPs
draft-tsaad-mpls-p2mp-loose-path-reopt-00.txt
Abstract
This document defines signaling extensions to Resource
Reservation Protocol - Traffic Engineering (RSVP-TE) for reoptimizing
loosely routed point-to-multipoint (P2MP) Traffic Engineered (TE)
Label Switched Path (LSP) in an Multi-Protocol Label Switching (MPLS)
and Generalized MPLS (GMPLS) networks.
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
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material or to cite them other than as "work in progress."
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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. Procedure for Reoptimization of a Loosely Routed P2MP-TE LSP . 4
4. RSVP Signaling Extensions . . . . . . . . . . . . . . . . . . . 5
4.1. P2MP-TE Tree Re-evaluation Request . . . . . . . . . . . . 5
4.2. Preferable P2MP-TE Tree Exists Error sub-code . . . . . . 5
5. Compatibility . . . . . . . . . . . . . . . . . . . . . . . . 6
6. Security Considerations . . . . . . . . . . . . . . . . . . . 6
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
7.1 P2MP-TE Tree Re-evaluation Request Flag . . . . . . . . . . 6
7.2 Preferable P2MP-TE Tree Exists sub-code . . . . . . . . . . 7
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 7
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7
8.1. Normative References . . . . . . . . . . . . . . . . . . . 7
8.2. Informative References . . . . . . . . . . . . . . . . . . 7
Author's Addresses . . . . . . . . . . . . . . . . . . . . . . . . 8
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1. Introduction
This document defines RSVP signaling extensions for the
reoptimization of loosely routed point-to-multipoint (P2MP) MPLS and
GMPLS (Generalized Multiprotocol Label Switching) Traffic Engineered
(TE) Label Switched Path (LSP).
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 at the time of its signaling by the
ingress node. Such an S2L sub-LSP is signaled with no Explicit Route
Object (ERO), 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).
[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. The ingress
node upon receiving this PathErr initiates reoptimization of the LSP.
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] 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. In addition, 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. Furthermore, when the ingress node gradually receives
unsolicited PathErr(s) notifications for individual S2L sub-LSP(s),
it may prematurely start reoptimizing these sub-set of 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(s) notifications for all S2L sub-
LSP(s) of the P2MP-TE LSP tree. In such cases, the ingress node may
have to heuristically determine when to perform P2MP-TE LSP tree
reoptimization or per S2L sub-LSP reoptimization, for example, to
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wait long enough time to accumulate all PathErr(s) to be received.
Such methods may produce undesired results that can be avoided by the
proposed RSVP signaling extensions in this draft.
This document defines required RSVP signaling extensions to query and
notify 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].
3. Procedure for Reoptimization of a Loosely Routed P2MP-TE LSP
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").
Procedures defined in [RFC4736] are used by an ingress node to
reoptimize the S2L sub-LSP individually.
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To reoptimize 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.
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 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 can be found, the
recommended mode is for the border node to relay the request (by
setting the "P2MP-TE Tree Re-evaluation Request" bit in the
LSP_ATTRIBUTES TLV of RSVP path message sent downstream).
A border node MAY also send "Preferable P2MP-TE Tree Exists" with
PathErr code 25 to the ingress node to reoptimize the entire P2MP-TE
LSP tree with an unsolicited PathErr message.
4. RSVP Signaling Extensions
4.1. P2MP-TE Tree Re-evaluation Request
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 an S2L sub-LSP and is inserted by the ingress node.
4.2. Preferable P2MP-TE Tree Exists 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
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When a preferable P2MP-TE LSP tree is found, the border node MUST
send "Preferable P2MP-TE Tree Exists" PathErr to the ingress node in
order to reoptimize the entire 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,
unexamined and unmodified, in all messages resulting from this
message.
6. Security Considerations
This document does not introduce any additional security issues above
those identified in [RFC3209] and [RFC4875].
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 (sections 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
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7.2 Preferable P2MP-TE Tree Exists 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.
8. References
8.1. 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.
8.2. 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.
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Author's Addresses
Tarek Saad
Cisco Systems
Email: tsaad@cisco.com
Rakesh Gandhi
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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