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Network Working Group Request for Comments: 4577 Updates: 4364 Category: Standards Track

E. Rosen P. Psenak P. Pillay-Esnault 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 andsuggestions 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 whichcustomer 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 VPNspresumes 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 Contents1. 2. 3. 4. Introduction ....................................................2 Specification of Requirements ...................................3 Requirements ....................................................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. RouterID ..........................................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 ......................134.2.6. 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 IANA Considerations ............................................22 Security Considerations ........................................23 Acknowledgements ...............................................23 Normative References...........................................23 Informative References .........................................24

5. 6. 7. 8. 9. 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...