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OSPF as the Provider/Customer Edge Protocol for BGP/MPLS IP Virtual Private Networks (VPNs)
RFC 4577

Network Working Group                                           E. Rosen
Request for Comments: 4577                                     P. Psenak
Updates: 4364                                          P. Pillay-Esnault
Category: Standards Track                            Cisco Systems, Inc.
                                                               June 2006

            OSPF as the Provider/Customer Edge Protocol for
              BGP/MPLS IP Virtual Private Networks (VPNs)

Status of This Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2006).

Abstract

   Many Service Providers offer Virtual Private Network (VPN) services
   to their customers, using a technique in which customer edge routers
   (CE routers) are routing peers of provider edge routers (PE routers).
   The Border Gateway Protocol (BGP) is used to distribute the
   customer's routes across the provider's IP backbone network, and
   Multiprotocol Label Switching (MPLS) is used to tunnel customer
   packets across the provider's backbone.  This is known as a "BGP/MPLS
   IP VPN".  The base specification for BGP/MPLS IP VPNs presumes that
   the routing protocol on the interface between a PE router and a CE
   router is BGP.  This document extends that specification by allowing
   the routing protocol on the PE/CE interface to be the Open Shortest
   Path First (OSPF) protocol.

   This document updates RFC 4364.

Rosen, et al.               Standards Track                     [Page 1]
RFC 4577               OSPF for BGP/MPLS IP VPNs               June 2006

Table of Contents

   1. Introduction ....................................................2
   2. Specification of Requirements ...................................3
   3. Requirements ....................................................4
   4. BGP/OSPF Interaction Procedures for PE Routers ..................6
      4.1. Overview ...................................................6
           4.1.1. VRFs and OSPF Instances .............................6
           4.1.2. VRFs and Routes .....................................6
           4.1.3. Inter-Area, Intra-Area, and External Routes .........7
           4.1.4. PEs and OSPF Area 0 .................................8
           4.1.5. Prevention of Loops .................................9
      4.2. Details ....................................................9
           4.2.1. Independent OSPF Instances in PEs ...................9
           4.2.2. Router ID ..........................................10
           4.2.3. OSPF Areas .........................................10
           4.2.4. OSPF Domain Identifiers ............................10
           4.2.5. Loop Prevention ....................................12
                  4.2.5.1. The DN Bit ................................12
                  4.2.5.2. Use of OSPF Route Tags ....................12
                  4.2.5.3. Other Possible Loops ......................13
           4.2.6. Handling LSAs from the CE ..........................14
           4.2.7. Sham Links .........................................16
                  4.2.7.1. Intra-Area Routes .........................16
                  4.2.7.2. Creating Sham Links .......................17
                  4.2.7.3. OSPF Protocol on Sham Links ...............18
                  4.2.7.4. Routing and Forwarding on Sham Links ......19
           4.2.8. VPN-IPv4 Routes Received via BGP ...................19
                  4.2.8.1. External Routes ...........................20
                  4.2.8.2. Summary Routes ............................22
                  4.2.8.3. NSSA Routes ...............................22
   5. IANA Considerations ............................................22
   6. Security Considerations ........................................23
   7. Acknowledgements ...............................................23
   8. Normative References ...........................................23
   9. Informative References .........................................24

1.  Introduction

   [VPN] describes a method by which a Service Provider (SP) can use its
   IP backbone to provide a VPN (Virtual Private Network) service to
   customers.  In that method, a customer's edge devices (CE devices)
   are connected to the provider's edge routers (PE routers).  If the CE
   device is a router, then the PE router may become a routing peer of

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