MPLS Working Group Tarek Saad, Ed.
Internet-Draft Rakesh Gandhi, Ed.
Intended status: Standards Track Zafar Ali
Expires: January 22, 2015 Cisco Systems, Inc.
Robert H. Venator
Defense Information Systems Agency
Yuji Kamite
NTT Communications Corporation
July 21, 2014
Reoptimization of Point-to-Multipoint Traffic Engineering
Loosely Routed LSPs
draft-tsaad-mpls-p2mp-loose-path-reopt-03
Abstract
For a Traffic Engineered (TE) point-to-multipoint (P2MP) Label
Switched Path (LSP), it is preferable in some cases to re-evaluate
and re-optimize the entire P2MP-TE LSP by re-signaling all its S2L
sub-LSP(s). Existing mechanisms allow the path re-evaluation and the
signaling of a the notification of preferred path exists for a single
S2L sub-LSP only.
This document defines RSVP-TE signaling extensions to allow an
ingress Label Switching Router (LSR) of a P2MP-TE LSP to trigger the
re-evaluation of the entire LSP tree containing one or more S2L sub-
LSPs whose paths are loose (or abstract) hop expanded, and for a mid-
point LSR to signal to the ingress LSR that a better tree exists for
the entire P2MP-TE LSP.
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."
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Copyright Notice
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1. Abbreviations . . . . . . . . . . . . . . . . . . . . . . 4
2.2. Nomenclatures . . . . . . . . . . . . . . . . . . . . . . 5
2.3. Conventions used in this document . . . . . . . . . . . . 5
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 . . . . . . . . . . . . . . . . . . . . . . . . 7
6. Security Considerations . . . . . . . . . . . . . . . . . . . 7
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
7.1. P2MP-TE Tree Re-evaluation Request Flag . . . . . . . . . 8
7.2. Preferable P2MP-TE Tree Exists Path Error sub-code . . . . 8
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 8
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9
9.1. Normative References . . . . . . . . . . . . . . . . . . . 9
9.2. Informative References . . . . . . . . . . . . . . . . . . 9
Author's Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10
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1. Introduction
This document defines Resource Reservation Protocol - Traffic
Engineering (RSVP-TE) [RFC2205] [RFC3209] signaling extensions for
re-optimizing loosely routed Point-to-Multipoint (P2MP) Traffic
Engineered (TE) Label Switched Paths (LSPs) [RFC4875] in an
Multi-Protocol Label Switching (MPLS) and/or Generalized MPLS (GMPLS)
networks.
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 re-optimize the entire P2MP-TE
LSP by re-signaling all its S2L sub-LSP(s) or may re-optimize
individual S2L sub-LSP(s) i.e. individual destination(s).
[RFC4736] defines RSVP signaling extensions for re-optimizing loosely
routed P2P TE LSP(s) as follows.
- A mid-point LSR that expands loose next-hop(s) MAY send a solicited
or unsolicited PathErr with the Notify error code (25 as defined in
[RFC3209]) with sub-code 6 to indicate "Preferable Path Exists" to
the ingress node.
- An ingress node MAY trigger a path re-evaluation request at all
mid-point LSR(s) that expands loose next-hop(s) by setting the "Path
Re-evaluation Request" flag (0x20) in SESSION_ATTRIBUTES object in
the Path message.
- The ingress node upon receiving this PathErr either solicited or
unsolicited initiates re-optimization of the LSP.
[RFC4736] does not define signaling extensions specific for re-
optimizing entire P2MP-TE LSP tree. Mechanisms defined in [RFC4736]
can be used for signaling the re-optimization of individual S2L sub-
LSP(s). However, to use [RFC4736] mechanisms for re-optimizing an
entire P2MP-TE LSP tree, an ingress node needs to send the path re-
evaluation requests on all (typically 100s of) S2L sub-LSPs and the
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mid-point LSR to notify PathErrs for all S2L sub-LSPs. Such a
procedure may lead to the following issues:
- A mid-point LSR that expands loose next-hop(s) may have to
accumulate the received path re-evaluation request(s) for all S2L
sub-LSPs (e.g, by using a wait timer) and interpret them as a re-
optimization request for the whole P2MP-TE LSP tree. Otherwise, A
mid-point LSR may prematurely notify "Preferable Path Exists" for one
or a sub-set of S2L sub-LSPs.
- The ingress LSR that receives (un)solicited PathErr notification(s)
for individual S2L sub-LSP(s), may prematurely start re-optimizing
the sub-set of S2L sub-LSPs. However, as mentioned in [RFC4875]
Section 14.2, such re-optimization procedure may result in data
duplication that can be avoided if the entire P2MP-TE LSP tree is re-
optimized, 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 re-optimization versus per S2L sub-
LSP re-optimization, for example, to delay re-optimization long
enough to allow all PathErr(s) to be received. Once all PathErr(s)
are received, the ingress node has to accumulate them to see if re-
optimization of the entire P2MP-TE is necessary. Such procedures may
produce undesired results due to timing related issues. This may be
easily avoided by the RSVP signaling messages defined in this
document.
This document defines RSVP-TE signaling extensions for the head-end
LSR of a P2MP-TE LSP to trigger the re-evaluation of the P2MP tree on
every hop that has a next hop defined as a loose or abstract hop for
one or more S2L sub-LSP path, and a mid-point LSR to signal to the
head-end LSR that a better tree exists (compared to the current path)
or that the whole P2MP-TE LSP must be re-optimized (because of
maintenance required on the TE LSP path).
2. Terminology
2.1. Abbreviations
ABR: Area Border Router.
AS: Autonomous System.
ERO: Explicit Route Object.
TE LSP: Traffic Engineering Label Switched Path.
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TE LSP ingress: head/source of the TE LSP.
TE LSP egress: tail/destination of the TE LSP.
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2.2. Nomenclatures
Domain: Routing or administrative domain such as an IGP area and an
autonomous system.
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).
S2L sub-LSP: Source-to-leaf sub Label Switched Path.
2.3. 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. Signaling Procedure For Loosely Routed P2MP-TE LSP Re-Optimization
It might be preferable, as per [RFC4875], to re-optimize the entire
P2MP-TE LSP by re-signaling all of its S2L sub-LSP(s) (Section 14.1,
"Make-before- Break") or re-optimize individual S2L sub-LSP(s) i.e.
individual destination(s) (Section 14.2 "Sub-Group-Based Re-
Optimization"). This can be achieved by using the procedures defined
in [RFC4736] to individually re-optimize the S2L sub-LSP(s) of a
P2MP-TE LSP.
To evaluate an entire P2MP-TE LSP tree on mid-point LSRs that expand
loose next-hop(s), an ingress node may send 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 to trigger the re-evaluation request(s).
A mid-point LSR that expands loose next-hop(s) for one or more S2L
sub-LSP path(s), and that receives a Path message with the "P2MP-TE
Tree Re-evaluation Request" bit set, checks for a preferable P2MP-TE
LSP tree by re-evaluating all S2L sub-LSP(s) expanded paths of the
P2MP-TE LSP. If a preferable P2MP-TE LSP tree is found, the mid-
point LSR 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". The mid-point LSR, in
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turn, does not propagate the "P2MP-TE Tree Re-evaluation Request" 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. In
addition, a mid-point LSR may send an unsolicited PathErr message
with "Preferable P2MP-TE Tree Exists" PathErr code 25 to the ingress
node to notify of a preferred the P2MP-TE LSP tree when it determines
it exists. In this case, the mid-point LSR that expands loose next-
hop(s) for one or more S2L sub-LSP path(s) may select one or more S2L
sub-LSP(s) of the P2MP-TE LSP tree to send this PathErr message to
the ingress node.
If no preferable tree for P2MP-TE LSP can be found, the recommended
mode is for the mid-point LSR that expands loose next-hop(s) for one
or more S2L sub-LSP path(s) to propagate the request downstream by
setting the "P2MP-TE Tree Re-evaluation Request" bit in the
LSP_ATTRIBUTES object of RSVP Path message.
4. RSVP Signaling Extensions
4.1. P2MP-TE Tree Re-evaluation Request Flag
In order to trigger a tree re-evaluation request, 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 exists, the 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 exists, the mid-point LSR
sends a solicited or unsolicited "Preferable P2MP-TE Tree Exists"
PathErr notification to the ingress node of the P2MP-TE LSP.
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5. Compatibility
The LSP_ATTRIBUTES object 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 defines a mechanism for a mid-point LSR to notify the
ingress node of a P2MP-TE LSP of the existence of a preferable tree.
As per [RFC4736], in the case of a P2MP-TE LSP S2L sub-LSP spanning
multiple domains, it may be desirable for a a mid-point LSR to modify
the RSVP PathErr message defined in this document to maintain
confidentiality across different domains. Furthermore, an ingress
node may decide to ignore this PathErr message coming from a mid-
point LSR residing in another domain. Similarly, an mid-point LSR
may decide to ignore the tree re-evaluation request originating from
another ingress domain.
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).
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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 value is to be assigned
by IANA.
o P2MP-TE Tree Re-evaluation Request Flag:
+--------+---------------+---------+---------+---------+------------+
| Bit No | Attribute | Carried | Carried | Carried | Reference |
| | Flag Name | in Path | in Resv | in RRO | |
+--------+---------------+---------+---------+---------+------------+
| TBA by | P2MP-TE Tree | Yes | No | No | This |
| IANA | Re-evaluation | | | | document |
+--------+---------------+---------+---------+---------+------------+
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 | Sub-code | PathErr | PathErr | Reference |
| value | Name | Code | Name | |
+----------+--------------------+---------+---------+-----------+
| TBA by | Preferable P2MP-TE | 25 | Notify | This |
| IANA | Tree Exists | | error | document |
+----------+--------------------+---------+---------+-----------+
8. Acknowledgments
The authors would like to thank Loa Andersson for reviewing this
document.
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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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