One document matched: draft-ali-mpls-inter-domain-p2mp-rsvp-te-lsp-04.txt

Differences from draft-ali-mpls-inter-domain-p2mp-rsvp-te-lsp-03.txt

MPLS Working Group                                           Z. Ali, Ed.
Internet-Draft                                       Cisco Systems, Inc.
Intended status: Standards Track                                N. Neate
Expires: September 7, 2010                           Data Connection Ltd
                                                        March 08, 2010

       Signaling RSVP-TE P2MP LSPs in an Inter-domain Environment
          draft-ali-mpls-inter-domain-p2mp-rsvp-te-lsp-04.txt

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Copyright

   Copyright (c) 2010 IETF Trust and the persons identified as the
   document authors. All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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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).


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  Conventions used in this document  . . . . . . . . . . . .  4
   2.  Framework  . . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  RSVP-TE signaling extensions . . . . . . . . . . . . . . . . .  4
     3.1.  SIBLING_S2L object . . . . . . . . . . . . . . . . . . . .  4
       3.1.1.  Format . . . . . . . . . . . . . . . . . . . . . . . .  4
       3.1.2.  Processing . . . . . . . . . . . . . . . . . . . . . .  7
     3.2.  Grafting . . . . . . . . . . . . . . . . . . . . . . . . .  7
     3.3.  Crankback and Path Error . . . . . . . . . . . . . . . . .  8
   4.  Security Considerations  . . . . . . . . . . . . . . . . . . .  8
   5.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  9
   6.  References . . . . . . . . . . . . . . . . . . . . . . . . . .  9
     6.1.  Normative References . . . . . . . . . . . . . . . . . . .  9
     6.2.  Informative References . . . . . . . . . . . . . . . . . .  9
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . .  9
   Intellectual Property and Copyright Statements . . . . . . . . . . 10

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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
   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 overall P2MP LSP is 
   re-merge free.



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   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
   mechanisms for P2MP LSPs are not addressed by [RFC4875].  This
   document also describes how crankback signaling extensions for MPLS
   and GMPLS RSVP-TE defined in [RFC4920] apply to setting up P2MP TE
   LSPs.

   The solution also 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

   TBA


3.  signaling procedure

   The ingress node can make sure that overall P2MP path traveling 
   multiple domain is remerge free by choosing single Ingress ABR/ ASBR
   for loose hop expension for all siblings of a P2MP LSPs.    

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3.3.  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.

   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.

   If a node on the path of the P2MP LSP is unable to find a route that
   can supply the required resources or is not 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.
   GMPLS 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 should attempt to re-route
   according to the crankback procedures defined in [RFC4920].  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 usptream.  The first node through which all S2L sub-LSPs
   concerned transit which receives the Path Error and is allowed to
   perform crankback procedures should re-route the S2L sub-LSPs
   concerned to all use the same border node.


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.





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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.

   [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
              Tunnels", RFC 3209, December 2001.


Authors' Addresses

   Zafar Ali (editor)
   Cisco Systems, Inc.
   Email: zali@cisco.com


   Nic Neate
   Data Connection Ltd
   100 Church Street
   Enfield  EN2 6BQ
   United Kingdom
   Email: nhn@dataconnection.com





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