Internet DRAFT - draft-mjsraman-pce-inter-as-p2mp-protect

draft-mjsraman-pce-inter-as-p2mp-protect



 



PCE Working Group                                          Shankar Raman
Internet draft                                             Balaji Venkat
Intended Status: Experimental RFC                           Gaurav Raina
Expires: July 2013                                         I.I.T, Madras
                                                        January 25, 2013


 Constructing protection paths for inter-AS, inter-sub-AS P2MP TE-LSPs
              draft-mjsraman-pce-inter-as-p2mp-protect-03


Abstract

   Constructing primary and backup explicit path Point-to-Multipoint
   Label Switched Paths is important from the point of view of providing
   protection switching in case the primary fails.

   It is absolutely essential that the backup P2MP LSPs constructed do
   not share risk with any of the links and nodes of the primary path.
   In the case of inter-AS P2MP TE-LSPs or in the case of inter-sub-AS
   (in the case of BGP-Confederations being deployed) P2MP TE-LSPs where
   BGP confederations are deployed within an AS, such protection
   switching can be provided by calculating primary and backup multicast
   distribution trees (read P2MP TE-LSPs) that dont intersect with each
   other.

   In this paper we propose a method by which inter-sub-AS P2MP TE-LSPs
   (hence even inter-AS P2MP TE-LSPs) can be constructed by first
   finding the AS level topology of the network (be it inter-AS or
   inter-sub-AS within a single AS) in question and secondly to compute
   the paths in such a way that they dont intersect or if necessary in
   the worst case partially intersect each other. The proposed scheme is
   explained with an example and subsequent discussion is done to
   elucidate its benefits to multicast in particular. 


Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as
   Internet-Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
 


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   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/1id-abstracts.html

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Copyright and License Notice

   Copyright (c) 2013 IETF Trust and the persons identified as the
   document authors. All rights reserved.

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   described in the Simplified BSD License.



Table of Contents

   1  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1  Terminology . . . . . . . . . . . . . . . . . . . . . . . .  3
   2  Methodology of the proposal . . . . . . . . . . . . . . . . . .  3
   3  Discussion  . . . . . . . . . . . . . . . . . . . . . . . . . .  8
     3.1 Discussion of Algorithms to be used  . . . . . . . . . . . .  9
   4  Security Considerations . . . . . . . . . . . . . . . . . . . . 11
   5  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 11
   6  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 11
     6.1  Normative References  . . . . . . . . . . . . . . . . . . . 11
     6.2  Informative References  . . . . . . . . . . . . . . . . . . 12
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13








 


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1  Introduction

   In the context of P2MP TE-LSPs being constructed for carriage of
   multicast traffic across multiple areas within a given AS employing
   BGP confederations  where such an autonomous system  may comprise of
   more than one BGP confederation instance, and if such multicast
   traffic is mission critical traffic then it would be most useful to
   have backup protection trees (where such trees represent entire P2MP
   TE-LSPs rooted at the same BGP confederation instance as the primary)
   or sub-trees which cover certain areas of the primary P2MP TE-LSP.
   The intent is to provide a solution whereby a backup protection P2MP
   TE-LSP can be laid out in such a way that the set of BGP
   confederation instances traversed by the primary (except say for the
   egress BGP confederation  instances) inter-sub-AS P2MP TE-LSP is not 
   traversed at all by the backup P2MP TE-LSP.  It is also possible that
   if such a totally distinct backup TE-LSP is not possible, then an
   effort be made where possible to construct a partially disjoint
   backup P2MP TE-LSP which tries to avoid to the extent possible those
   BGP confederation instances  which fall in the primary.

   While this type of a solution is available in the unicast world
   applying to inter-AS cases  such a solution doesn't  seem to have
   been proposed for the multicast world for inter-AS P2MP TE-LSPs or
   for cases within an autonomous system in which BGP conferderations
   are deployed.


1.1  Terminology

   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 [RFC2119].


2  Methodology of the proposal

   Assume that a centralized path calculation engine is available as a
   facility in the head end BGP confederation instance of the P2MP TE-
   LSP. And this centralized PCE has a backup PCE that does pretty much
   the same work as the primary PCE in the head end BGP confederation
   instance  except that it is not contacted for path calculation
   requests while the active is still up. At the active PCE the
   following happens. The intention at the active PCE is to gather all
   routes advertised by BGP peers internal and external/internal (a.k.a
   EIBGP used for confederations) and collect from each of these routes
   the AS path information attribute (which is a mandatory well-known)
   and from each of these AS path info attributes which we will call
   strands from now on, an entire BGP-confederation-instance-Level
 


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   topology of the AS involved (in the case of inter-AS the internet) is
   captured to the extent possible. These strands give us information
   about sections of a BGP-confederation-instance level graph, where
   each BGP-confederation-instance is considered to be a node and the
   edge is connectivity between two or more such confederation-
   instances. Where a set of BGP-confederation-instances are consecutive
   in a strand they are assumed to be connected to each other.

   It is to be noted that the information about such strands may come
   from iBGP, eiBGP, MBGP (in the case of inter-AS level) (sometimes
   known as Multi-protocol BGP used for multicast) if it carries AS path
   information. After the BGP-confederation-instance level topology of
   the immediate neighborhood of the ingress BGP-confederation instance
   and the egress BGP-confederation-instances to which the multicast
   subscribers connect to, has been constructed, the P2MP TE-LSP
   calculation algorithm is run, that takes into account a path in the
   topology that is most optimal to help and connect the source to the
   destinations / receivers. It is possible that source and receivers
   who may be distributed across multiple BGP-confederation-instances in
   the neighborhood are multihomed in that they have more than one BGP-
   confederation instance to which they are connected to. This is
   particularly of interest to the algorithm presented in this invention
   (in summary) because the backup P2MP TE-LSP needs to be spread out
   across links that are disjoint from the primary P2MP TE-LSP to the
   extent possible and multi-homing in this case helps a great deal.

   Once the primary has been built and the secondary is sought to be
   built, the invention proposed would take into account multi-homing
   characteristics of the egress BGP-confederation instances to their
   respective receivers (which may be enterprise networks / sites) and
   build a totally disjoint P2MP TE-LSP or if that is not possible a
   partially disjoint P2MP TE-LSPs. It is also possible that manual
   policies may be stated in a suitable format to avoid certain BGP-
   confederation-instances in the calculation of either a totally
   disjoint or partially disjoint backup P2MP TE-LSP.

   It is assumed that RSVP-TE would be used to build such primary and
   secondary P2MP TE-LSPs be they disjoint or partially disjoint.

   Building a BGP-confederation-instance topology of the immediate
   neighborhood of the ingress and egress BGP-confederation-instance for
   a multicast tree to carry one or more streams of mcast traffic
   through such a tree.





 


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   Here the term AS refers to a BGP-confederation-instance.

   Prefix-A: AS-Path Info: AS1  AS2   AS4
   Prefix-B: AS-Path Info: AS2  AS3   AS4
   Prefix-C: AS-Path Info: AS2  AS5   AS6    and so on.

   Figure 1.0 Strand obtained from a subgraph of the AS having
   confederations

   Given the above three strands of information we could build out the
   following graph.

               AS5---------> AS6
               |
   AS1 ----->  AS2 --------> AS4
               |            /
               --------> AS3

   Figure 2.0 Strands put together to form a graph of the AS with
   confederations

   If we extrapolate this to a number of such prefixes and their
   respective AS paths we could end up discovering the BGP-
   confederation-instance level topology for a greater radius than is
   otherwise possible with the ingress BGP-confederation-instance to
   which the source is connected as the center.

   Multi-homing links appear as duplicate edges between receivers /
   source to their respective egress / ingress BGP-confederation-
   instances. Thus building out disjoint and partially disjoint P2MP TE-
   LSPs using RSVP-TE is a helpful technique in protecting mission
   critical multicast traffic on the primary by obviating the need for
   fate-sharing of the path that such traffic takes to the extent
   possible.


   Assume that the following BGP-confederation-instance topology in the
   vicinity of the sender / senders is computed.










 


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                   +----------------+
                  /                 V
                 /         +----> (AS2) ------> (AS3)<--(RcvrB)
                /         /                      \         |
               /         /                        \ +------+
              /         /                          \V
         (source/s)--->(AS1)------> (AS5) ------> (AS4)<-(RcvrA)
                        \                         /\       /
                         \             ----------+  \     /
                          \           /              \   /
                         (AS6)----> (AS7) ------> (AS8)<+

   Figure 3.0 Strands put together to form a graph of the AS with
   confederations


   In the above diagram you can see that the source/sources are
   connected using a multi homed connections to the same ISP through
   BGP-confederation instance AS1 and AS2. Similarly there are two
   Receiver sites RcvrA and RcvrB that are multihomed to TWO BGP-
   confederation-instances for RcvrB to AS3 and AS4 and for RcvrA to AS4
   and AS8 respectively.


   Given that the path calculation engine in AS1 BGP-confederation-
   instance is given this picture as it absorbs the AS paths and builds
   out the BGP-confederation-instances level topology, there are at
   least 2 possible completely (to the maximum extent possible) disjoint
   P2MP TE-LSPs possible. Note here of course that the egress BGP-
   confederation-instance sometimes prevents a totally disjoint P2MP TE-
   LSP since the two up-until-the-egress-BGP-confederation-instance
   totally P2MP TE-LSPs may be need to merge to enter the receiver
   domains / sites.

   They are illustrated below.

   Primary P2MP TE-LSP advised could be as illustrated by the dotted
   lines...










 


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                   +----------------+
                  /                 V
                 /         +----> (AS2) ------> (AS3)<--(RcvrB)
                /         /                      \         |
               /         /                        \ +------+
              /         /                          \V
         (source/s)...>(AS1)------> (AS5) ------> (AS4)<-(RcvrA)
                        .                         .\       /
                         .             ...........  \     /
                          .           .              \   /
                         (AS6).....>(AS7) .......>(AS8)<+

   Figure 4.0 Strands put together to form a graph of the AS with
   confederations





   Secondary P2MP TE-LSP advicsed could be as illustrated by the dotted
   lines...
                   ..................
                  .                 V
                 .         +----> (AS2).......> (AS3)<--(RcvrB)
                .         /                      .         |
               .         /                        . +------+
              .         /                          .V
         (source/s)--->(AS1)------> (AS5) ------> (AS4)<-(RcvrA)
                        \                         /\       /
                         \             ----------+  \     /
                          \           /              \   /
                         (AS6)----> (AS7) ------> (AS8)<+



   It is important to note that multicast P2MP TE-LSPs constructed are
   considered to be stitched sections of unicast paths and may include
   multicast topologies reserved for multicast use alone that may have
   been advertised by Multi-protocol BGP just for multicast purposes (in
   the case of inter-AS). The normal mechanism of discovering receivers
   could be employed.

   It is to be noted that while constructing the BGP-confederation-
   instance-Level topology the routes which have been advertised in BGP
   that carry multicast NLRIs can be preferred and such inter-BGP-
   confederation-instance links can be given a higher priority for
   constructing the P2MP TE-LSPs. Please read the term AS in the
   following paras to represent a BGP-confederation instance.
 


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    It is to be noted that this applies to centralized schemes of path
   calculations. What is being calculated is a tree of ASes that form a
   P2MP tree where each node can conceptualized as an AS and each edge
   the border link connecting one AS to another to carry multicast
   traffic from several sources located at the head end ingress AS to
   several receiver nodes connected to egress ASes. We will call this
   calculated tree as a P2MP AS tree. Once the tree is calculated the
   PCE in the head end / ingress AS through which sources connect
   calculates the intra-AS P2MP path (the literal P2MP TE-LSP within the
   AS) within that ingress AS and hands off the elements in the P2MP AS
   tree in suitable form to the branch ASes which branch off from the
   ingress AS. This is followed as the information about the elements of
   the P2MP AS tree are handed off at branches from the PCE of one AS to
   another until the final inter-AS P2MP literal TE-LSP is complete. The
   backup P2MP AS tree is constructed as well and the same procedure is
   followed. This completes the construction of the primary and the
   backup P2MP AS Trees.

   The failover mechanism could be derived from any one of the available
   mechanisms in existence or a novel method for failover could also be
   deduced. But that is outside the scope of this document.

   This method could be applied for multicast traffic to be transported
   through L3VPNs and L2VPNs as well through such inter-AS tree
   construction of a P2MP AS tree. Also this method of constructing
   inter-AS disjoint P2MP AS trees is independent of how the egress ASes
   and the ingress AS are discovered. The method of such discovery is
   left to existing mechanisms. The primary input to the invention
   proposed is a list of ingress AS and their respective egress ASes.
   The other input to the construction of P2MP AS tree part of the
   invention of course is the BGP-confederation-AS-instance level
   topology (in case of inter-AS the AS level topology of the
   neighborhood).

   It is also possible to apply policies in such a way that the
   construction of the P2MP AS tree is done in a partially disjoint
   fashion. That is if there exist certain policies that dictate that a
   given AS in the path of the P2MP AS tree is to be present in both the
   primary and backup P2MP AS trees, then it would be applied at the PCE
   and the resultant tree would contain that AS as policy dictates. Thus
   the mechanism could churn out disjoint (totally) P2MP AS trees or
   partially disjoint P2MP AS trees depending on policy dictats.

3  Discussion


   A centralized picture of a AS level topology of the immediate
   vicinity of the egress and ingress ASes of a multicast tree to be
 


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   built using a P2MP TE LSP, helps build a backup P2MP TE-LSP  without
   traversing wherever possible the ASes in the primary for the backup

   Backup / protection switching is a lot more reliable since the fate-
   sharing is precluded to the maximum extent possible.

   Also the multi-homing characteristics of the sites / receivers  as
   well as the multi-homing characteristics of the source to its ingress
   PEs which may be located in different ISP ASes helps in building out
   a disjoint path that may well help in avoid in fate-sharing if an
   edge between two ASes or an AS itself goes down.

   Whether it be OPTIONS A,B or C as listed in the inter-AS RFCs the
   method we propose can be used to calculate the P2MP AS tree and the
   actual construction left to those methods applying to those options
   respectively.

   Multicast NLRI information could be used to give priority to routes
   learnt in that fashion and AS path information  used to construct the
   P2MP AS tree may be favourably passed through ASes listed within it.
   Thus if there exist in-congruent multicast and unicast topologies
   then this method could use the appropriate multicast topology hints
   apart from using the unicast topology information for constructing 
   P2MP AS trees that are more suited to multicast topology hints
   provided.

   AS sequences which are not ordered ASes representing AS paths toward
   a destination may be dropped from consideration while constructing
   the topology of ASes in the immediate neighborhood or in toto.

   This proposal will also be applicable to ASes which are independent
   administrative domains in a literal sense (as against BGP-
   confederation instances) as outlined.

3.1 Discussion of Algorithms to be used 

   The basic first cut algorithm that can be used for implementing this
   scheme is to account or collate the list of ASes the primary P2MP TE-
   LSP has passed through. These set of ASes can be enclosed in a set
   EXCLUDE_ASes and the algorithm for the secondary P2MP TE-LSP run with
   the constraint that any of the elements / ASes in this set are to be
   avoided. The set EXCLUDE_ASes is ordered with the branch points in
   order of traversal from the egress AS to the source ASes where the
   receivers are located. So the first check is applied for the elements
   / ASes in the beginning of the EXCLUDE_ASes set working backwards
   from the receivers to the source ASes. Only in cases where disjoint
   paths are not possible will the overlap occur. 

 


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   Another way is to weight the edges in the primary P2MP TE-LSP with
   higher weights and simply run the algorithm on the topology again. If
   the CSPF algorithm finds edges which are high it can be made to avoid
   such nodes and edges thus excluding the ASes in the primary path. The
   weights that can be assigned for the primary P2MP tree edges is 1/n
   where n was the lower weight for these edges when the primary P2MP
   LSP was constructed. All the edges in the graph are assigned 1/n as
   well. This way the lowest weights of the previous run become the
   higher weights of the secondary run. Once this is done one could use
   graph clipping and rejoining as explained below. This algorithm too
   can run backwards from the egress ASes to the source AS.

   Another way is to use graph clipping and rejoining without coupling
   with the previous algorithm. The primary path ASes are simply clipped
   along with the edges from the graph at the PCE and the algorithm run
   again to build a P2MP TE-LSP covering all receivers. Notably if the
   receivers are multi-homed the primary P2MP TE-LSP ASes can be removed
   first for such cases. If they are single-homed then it would be
   worthwhile retaining such egress ASes for the second run. The re-run
   can then try to build the tree, and if incrementally such an attempt
   fails those ASes in the Primary P2MP TE-LSP which are necessarily
   needed in the secondary P2MP tree can be added to the secondary tree
   till the completion of the secondary P2MP TE-LSP occurs. So the CSPF
   would operate on the graph clipping first and then rejoining those
   ASes without which a secondary cannot be built. This again could be
   run backwards from the egress AS to the source AS.

   An intermediary meeting point akin to the Rendezvous point can be
   chosen such that the primary RP AS is disjoint from the secondary RP
   AS. Working backwards this will in most cases produce the optimal
   result. Further proof of this algorithm will be furnished in future
   versions of this document.
















 


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4  Security Considerations

   When receiving BGP updates from BGP-confederation-instances the PCE
   or the head end which is expected to do the calculation of the
   totally disjoint or partially disjoint P2MP TE-LSP paths MUST ensure
   the authenticity of the updates received from other BGP-
   confederation-instances through existing mechanisms that assure that
   the updates are not spoofed thus misleading the receiver of such
   updates. No additional security hole is seen under these
   circumstances apart from the above.


5  IANA Considerations

   No IANA requirements exist as of the time of writing of this draft.


6  References

6.1  Normative References

   [KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC1776]  Crocker, S., "The Address is the Message", RFC 1776, April
              1 1995.

   [TRUTHS]   Callon, R., "The Twelve Networking Truths", RFC 1925,
              April 1 1996.

   [RFC4875]  Aggarwal, R., Ed., Papadimitriou, D., Ed., and S.
              Yasukawa, Ed., "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., Ed., 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., Ed., Satyanarayana, A., Iwata, A., Fujita, N.,
              and G. Ash, "Crankback Signaling Extensions for MPLS and
              GMPLS RSVP-TE", RFC 4920, July 2007.

   [RFC5920]  Fang, L., Ed., "Security Framework for MPLS and GMPLS
              Networks", RFC 5920, July 2010.

 


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   [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.


6.2  Informative References

   [EVILBIT]  Bellovin, S., "The Security Flag in the IPv4 Header",
              RFC 3514, April 1 2003.

   [RFC5513]  Farrel, A., "IANA Considerations for Three Letter
              Acronyms", RFC 5513, April 1 2009.

   [RFC5514]  Vyncke, E., "IPv6 over Social Networks", RFC 5514, April 1
              2009.

   [RFC4726]  Farrel, A., Vasseur, J.-P., and A. Ayyangar, "A Framework
              for Inter-Domain Multiprotocol Label Switching Traffic
              Engineering", RFC 4726, November 2006.

   [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.
















 


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Authors' Addresses


   Shankar Raman
   Department of Computer Science and Engineering
   I.I.T Madras,
   Chennai - 600036
   TamilNadu,
   India.

   EMail: mjsraman@cse.iitm.ac.in



   Balaji Venkat Venkataswami
   Department of Electrical Engineering,
   I.I.T Madras,
   Chennai - 600036,
   TamilNadu,
   India.

   EMail: balajivenkat299@gmail.com



   Prof.Gaurav Raina
   Department of Electrical Engineering,
   I.I.T Madras,
   Chennai - 600036,
   TamilNadu,
   India.

   EMail: gaurav@ee.iitm.ac.in


















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