One document matched: draft-ali-mpls-inter-domain-p2mp-rsvp-te-lsp-05.txt
Differences from draft-ali-mpls-inter-domain-p2mp-rsvp-te-lsp-04.txt
MPLS Working Group Z. Ali, Ed.
Internet-Draft Cisco Systems, Inc.
Intended status: Standards Track N. Neate
Expires: April 24, 2011 Metaswitch Networks
October 25, 2010
Signaling RSVP-TE P2MP LSPs in an Inter-domain Environment
draft-ali-mpls-inter-domain-p2mp-rsvp-te-lsp-05.txt
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Abstract
Point-to-MultiPoint (P2MP) Multiprotocol Label Switching (MPLS) and
Generalized MPLS (GMPLS) Traffic Engineering Label Switched Paths (TE
LSPs) may be established using signaling techniques described in
[RFC4875]. However, [RFC4875] does not address issues that arise
when a P2MP-TE LSP is signaled in multi-domain networks.
Specifically, it does not provide a mechanism to avoid re-merges in
inter-domain P2MP TE LSPs. This document provides a framework and
protocol extensions for establishing and controlling P2MP MPLS and
GMPLS TE LSPs in multi-domain networks.
This document borrows inter-domain TE terminology from [RFC4726],
e.g., for the purposes of this document, a domain is considered to be
any collection of network elements within a common sphere of address
management or path computational responsibility. Examples of such
domains include Interior Gateway Protocol (IGP) areas and Autonomous
Systems (ASes).
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Conventions used in this document . . . . . . . . . . . . . 4
2. Framework . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1. Signaling Options . . . . . . . . . . . . . . . . . . . . . 4
2.2. Path Computation Techniques . . . . . . . . . . . . . . . . 4
3. Signaling Procedures . . . . . . . . . . . . . . . . . . . . . 5
3.1. Crankback and Path Error . . . . . . . . . . . . . . . . . 5
4. Security Considerations . . . . . . . . . . . . . . . . . . . . 6
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6
6.1. Normative References . . . . . . . . . . . . . . . . . . . 6
6.2. Informative References . . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 7
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1. Introduction
[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.
As with all other RSVP controlled LSPs, P2MP LSP state is managed
using RSVP messages. While the use of RSVP messages is mostly
similar to their P2P counterpart, P2MP LSP state differs from P2P LSP
in a number of ways. In particular, the P2MP LSP must also handle
the "re-merge" problem described in [RFC4875] section 18.
The term "re-merge" refers to the situation when two S2L sub-LSPs
branch at some point in the P2MP tree, and then intersect again at a
another node further down the tree. This may occur due to
discrepencies in the routing algorithms used by different nodes,
errors in path calculation or manual configuration, or network
topology changes during the establishment of the P2MP LSP. Such re-
merges are inefficient due to the unnecessary duplication of data.
Consequently one of the requirements for signaling P2MP LSPs is to
choose a P2MP path that is re-merge free. In some deployments, it
may also be required to signal P2MP LSPs that are both re-merge and
crossover free [RFC4875].
This requirement becomes more acute to address when P2MP LSP spans
multiple domains. For the purposes of this document, a domain is
considered to be any collection of network elements within a common
sphere of address management or path computational responsibility.
Examples of such domains include Interior Gateway Protocol (IGP)
areas and Autonomous Systems (ASes). This is because in an inter-
domain environment, the ingress node may not have topological
visibility into other domains to be able to compute and signal a re-
merge free P2MP LSP. In that case, the border node for a new domain
will be given one or more loose next hops for the P2MP LSP. When
processing a path message, it may not have knowledge of all of the
destinations of the P2MP LSP, either because S2L sub-LSPs are split
between multiple Path messages, or because not all S2L sub-LSPs pass
through this border node. In that case, existing protocol mechanisms
do not provide sufficient information for it to be able to expand the
loose hop(s) in such a way that the overall P2MP path is guaranteed
to be optimal and re-merge free.
This document proposes a simple procedure such that the overall P2MP
LSP is re-merge free.
The need for finding an end-to-end path that is re-merge free also
increases chances of crankbacks during setting up P2MP LSPs as
compared to their P2P counterparts. Nonetheless, crankback
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mechanisms for P2MP LSPs are not addressed by [RFC4875]. [RFC5151]
describes mechanisms for applying crankback to inter-domain P2P LSPs,
but does not cover P2MP LSPs. This document therefore also describes
how crankback signaling extensions for MPLS and GMPLS RSVP-TE defined
in [RFC4920] apply to setting up P2MP TE LSPs.
The solution presented in this document does not guarantee
optimization of the overall P2MP tree across all domains. PCE can be
used, instead, to address optimization of the overall P2MP tree.
1.1. 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 RFC-2119.
2. Framework
2.1. Signaling Options
The four signaling options defined for P2P inter-domain LSPs in
[RFC4726] are also applicable to P2MP LSPs.
o LSP nesting, using hierarchical LSPs [RFC4206].
o A single contiguous LSP, using the same SESSION and LSP ID along
its whole path.
o LSP stitching [RFC5150].
o A combination of the above.
In the case of LSP nesting using hierarchical LSPs, the tunneled LSP
MUST use upstream-assigned labels to ensure that the same label is
used at every leaf of the H-LSP ([RFC5331],
[I-D.ietf-mpls-rsvp-upstream]). The H-LSP SHOULD request non-PHP
behavior and out-of-band mapping as defined in
[I-D.ietf-mpls-rsvp-te-no-php-oob-mapping].
2.2. Path Computation Techniques
This document focuses on the case where the headend does not have
full visibility of the topology of all domains, and is therefore not
able to compute the complete P2MP tree. Rather, it has to include
loose hops to traverse domains for which it does not have full
visibility, and the border node(s) on entry to each domain are
responsible for expanding those loose hops.
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3. Signaling Procedures
It is RECOMMENDED that boundary re-routing or segment-based re-
routing is requested for P2MP LSPs traversing multiple domains. This
is because border nodes that are expanding loose hops are typically
best placed to correct any re-merge errors that occur within their
domain, not the ingress node.
The ingress node is RECOMMENDED to select the same border node as an
ERO loose hop for all sibling S2L sub-LSPs that transit a given
domain. This reduces the chances of the sibling S2L sub-LSPs being
remerged, because a single border node has the necessary state to
ensure that the path that they take through the domain is remerge
free.
3.1. Crankback and Path Error
Crankback procedures for rerouting around failures for P2P RSVP-TE
LSPs are defined in [RFC4920]. These techniques can also be applied
to P2MP LSPs, as decribed in this section.
If a node on the path of the P2MP LSP is unable to find a route that
can supply the required resources or that is re-merge free, it SHOULD
generate a Path Error message for the subset of the S2L sub-LSPs
which it is not able to route. For this purpose the node SHOULD try
to find a minimum subset of S2L sub-LSPs for which the Path Error
needs to be generated. This rule applies equally to the case where
multiple S2L sub-LSPs are signaled using one Path message, as to the
case where a single S2L sub-LSP is signaled in each Path message.
RSVP-TE Notify messages do not include S2L_SUB_LSP objects and cannot
be used to send errors for a subset of the S2L sub-LSPs in a Path
message. For that reason, the node SHOULD use a Path Error message
rather than a Notify message to communicate the error. In the case
of a re-merge error, the node SHOULD use the error code "Routing
Problem" and the error value "ERO resulted in re-merge" as specified
in [RFC4875].
A border node receiving a Path Error message for a set of S2L sub-
LSPs MAY hold the message and attempt to signal an alternate path
through its domain for those S2L LSPs that pass through it. However,
in the case of a re-merge error for which some of the re-merging S2L
sub-LSPs do not pass through the border node, it SHOULD propagate the
Path Error upstream to the ingress node. If the subsequent attempt
is successful, the border node discards the held Path Error. If all
subsequent attempts are unsuccessful, the border node SHOULD send the
held Path Error upstream to the ingress node.
If the ingress node receives a Path Error message with error code
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"Routing Problem" and error value "ERO resulted in re-merge", then it
SHOULD attempt to signal an alternate path through a different domain
for the affected S2L sub-LSPs.
4. Security Considerations
Security considerations and requirements from [RFC4875] and [RFC4875]
apply equally to this document. Furthermore, there are some
additional security considerations that may be induced by the use of
"Related Addresses for Sibling S2L sub-LSP" object defined in this
document. These security considerations will be added in a later
version of the draft.
5. IANA Considerations
Code points for "Related Addresses for Sibling S2L sub-LSP" object
defined in this document will be required. Much of the details here
are TBA.
6. References
6.1. Normative References
[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.
[RFC5151] Farrel, A., Ayyangar, A., and JP. Vasseur, "Inter-Domain
MPLS and GMPLS Traffic Engineering -- Resource Reservation
Protocol-Traffic Engineering (RSVP-TE) Extensions",
RFC 5151, February 2008.
[RFC4920] Farrel, A., Satyanarayana, A., Iwata, A., Fujita, N., and
G. Ash, "Crankback Signaling Extensions for MPLS and GMPLS
RSVP-TE", RFC 4920, July 2007.
6.2. Informative References
[RFC4726] Farrel, A., Vasseur, J., and A. Ayyangar, "A Framework for
Inter-Domain Multiprotocol Label Switching Traffic
Engineering", RFC 4726, November 2006.
[RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
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Tunnels", RFC 3209, December 2001.
[RFC4206] Kompella, K. and Y. Rekhter, "Label Switched Paths (LSP)
Hierarchy with Generalized Multi-Protocol Label Switching
(GMPLS) Traffic Engineering (TE)", RFC 4206, October 2005.
[RFC5150] Ayyangar, A., Kompella, K., Vasseur, JP., and A. Farrel,
"Label Switched Path Stitching with Generalized
Multiprotocol Label Switching Traffic Engineering (GMPLS
TE)", RFC 5150, February 2008.
[RFC5331] Aggarwal, R., Rekhter, Y., and E. Rosen, "MPLS Upstream
Label Assignment and Context-Specific Label Space",
RFC 5331, August 2008.
[I-D.ietf-mpls-rsvp-upstream]
Aggarwal, R. and J. Roux, "MPLS Upstream Label Assignment
for RSVP-TE", draft-ietf-mpls-rsvp-upstream-05 (work in
progress), March 2010.
[I-D.ietf-mpls-rsvp-te-no-php-oob-mapping]
Ali, Z. and G. Swallow, "Non PHP Behavior and out-of-band
mapping for RSVP-TE LSPs",
draft-ietf-mpls-rsvp-te-no-php-oob-mapping-04 (work in
progress), March 2010.
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Authors' Addresses
Zafar Ali (editor)
Cisco Systems, Inc.
Email: zali@cisco.com
Nic Neate
Metaswitch Networks
100 Church Street
Enfield EN2 6BQ
United Kingdom
Email: nhn@metaswitch.com
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