One document matched: draft-rosen-ppvpn-ospf2547-area0-02.txt

Differences from draft-rosen-ppvpn-ospf2547-area0-01.txt

Network Working Group                                      Eric C. Rosen
Internet Draft                                              Peter Psenak
Expiration Date: August 2003                         Cisco Systems, Inc.

                                                    Padma Pillay-Esnault
                                                  Juniper Networks, Inc.

                                                           February 2003


                OSPF Area 0 PE/CE Links in BGP/MPLS VPNs


                draft-rosen-ppvpn-ospf2547-area0-02.txt

Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups. Note that other
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   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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   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt.

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

Abstract

   [VPN] describes a method of providing a VPN service.  That method
   allows a variety of different protocols to be used as the routing
   protocol between the Customer Edge (CE) router and the Provider Edge
   (PE) router.  [OSPF-VPN} specifies the procedures which must be
   implemented within the Provider's network when the PE/CE routing
   protocol is OSPF [OSPF], and the PE/CE link is not an area 0 link.
   This document specifies the additional, optional, procedures that
   must be implemented to support the case in which the PE/CE link is an
   area 0 link.





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Table of Contents

    1        Specification of Requirements  ........................   2
    2        Introduction  .........................................   2
    3        The VPN Backbone and Area 0  ..........................   3
    4        VPN-IP Routes Received via BGP  .......................   3
    5        Handling LSAs from the CE  ............................   4
    6        Sham Links  ...........................................   4
    7        Acknowledgments  ......................................   4
    8        Authors' Address  .....................................   4
    9        Normative References  .................................   5





1. Specification of Requirements

   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. Introduction

   [VPN] describes a method of providing a VPN service.  That method
   allows a variety of different protocols to be used as the routing
   protocol between the Customer Edge (CE) router and the Provider Edge
   (PE) router.  [OSPF-VPN} specifies the procedures which must be
   implemented within the Provider's network when the PE/CE routing
   protocol is OSPF [OSPF], and the PE/CE link is not an area 0 link.
   This document specifies the additional, optional, procedures that
   must be implemented to support the case in which the PE/CE link is an
   area 0 link.  Whereas the procedures of [OSPF-VPN] do not require any
   modifications to the OSPF protocol itself, the procedures specified
   herein do require a small OSPF protocol modification.

   The procedures specified herein are optional, and are additional to
   the procedures specified in [OSPF-VPN].

   CE routers, connected to PE routers of the VPN service, may
   themselves function as OSPF backbone (area 0) routers.  An OSPF
   backbone may even consist of several "segments" which are
   interconnected themselves only via the VPN service. In such a
   scenario, full intercommunication between sites connected to
   different segments of the OSPF backbone should still be possible.



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3. The VPN Backbone and Area 0

   As specified in [OSPF-VPN], every PE attached to a particular OSPF
   network MUST be an OSPF area 0 router.

   If the OSPF domain has any area 0 routers (other than the PE
   routers), then at least one of those MUST be a CE router, and MUST
   have an area 0 link to at least one PE router. This adjacency MAY be
   via an OSPF virtual link. This is necessary to ensure that inter-area
   routes and AS-external routes can be leaked between the PE routers
   and the non-PE OSPF backbone.

   Two sites which are not in the same OSPF area will see the VPN
   backbone as being an integral part of the OSPF backbone. However, if
   there are area 0 routers which are NOT PE routers, then the VPN
   backbone actually functions as a sort of higher level backbone,
   providing a third level of hierarchy above area 0.  This allows,
   e.g., a legacy OSPF backbone to become disconnected during a period
   of transition to a VPN, as long as the various segments of the OSPF
   backbone all attach to the VPN backbone.

   As specified in [OSPF-VPN], VPN-IP routes received by a PE via BGP
   may cause the PE to send type 3 LSAs to a CE router.  These type 3
   LSAs may eventually be redistributed by another CE router to another
   PE router.  If the link between the latter CE and the latter PE is
   not in area 0, then ordinary OSPF procedures cause those LSAs to be
   ignored, as in this case the PE is an ABR and an ABR does not forward
   type 3 LSAs that come from within a non-zero area.  Once we allow
   PE/CE links to be within area 0, it is possible that one PE will turn
   a BGP-distributed VPN-IP route into a type 3 LSA, and another PE will
   turn that type 3 LSA back into a BGP-distributed VPN-IP route.  If
   this is allowed, routing loops may form.  A procedure is therefore
   defined in this document which prevents this from happening.



4. VPN-IP Routes Received via BGP

   [OSPF-VPN] specifies various conditions under which the receipt of
   VPN-IP routes via BGP causes a PE to send a type 3 LSA to a CE.

   When a type 3 LSA is sent over an area 0 link from a PE router to a
   CE router, the high-order bit of the LSA Options field (previously
   unused) MUST be set.  We refer to this bit as the DN bit.  On PE/CE
   links which are not in area 0, the DN bit MAY be set.

   In all other respects, the procedures from [OSPF-VPN] section 4.2.4
   are followed.



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5. Handling LSAs from the CE

   When a PE router receives, from a CE router, a type 3 LSA with the DN
   bit set, the information from that LSA is not used by the SPF
   computation.

   In all other respects, the procedures from [OSPF-VPN} section 4.2.2
   are followed.


6. Sham Links

   Sham links may be created within area 0.



7. Acknowledgments

   Significant contributions to this work have been made by Derek Yeung
   and Yakov Rekhter.

   Thanks to Ross Callon and Ajay Singhal for their comments.


8. Authors' Address


   Eric C. Rosen
   Cisco Systems, Inc.
   250 Apollo Drive
   Chelmsford, MA, 01824

   E-mail: erosen@cisco.com



   Peter Psenak
   Parc Pegasus,
   De Kleetlaan 6A
   1831 Diegem
   Belgium

   E-mail: ppsenak@cisco.com








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   Padma Pillay-Esnault
   Juniper Networks
   1194 N. Mathilda Avenue
   Sunnyvale, CA 94089

   E-mail: padma@juniper.net



9. Normative References

   [EXT] "BGP Extended Communities Attribute", draft-ietf-idr-bgp-ext-
   communities-05.txt>,  Sangli, S., Tappan, D., Rekhter, Y., May 2002

   [OSPF] "OSPF Version 2", RFC 2328, Moy, J., April 1998.

   [VPN] "BGP/MPLS VPNs", draft-ietf-ppvpn-rfc2547bis-03.txt, Rosen, E.,
   et. al., October 2002.

   [OSPF-VPN] "OSPF as the PE/CE Protocol in BGP/MPLS VPNs", draft-
   rosen-vpns-ospf-bgp-mpls-06.txt, Rosen, E., et. all., February 2003





























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