This document provides a sample configuration of a Multiprotocol Label Switching (MPLS) Virtual Private Network (VPN) over ATM when Border Gateway Protocol (BGP) or Routing Information Protocol (RIP) is present on the customer's site.
When used with MPLS, the VPN feature allows several sites to interconnect transparently through a service provider's network. One service provider network can support several different IP VPNs. Each of these appears to its users as a private network, separate from all other networks. Within a VPN, each site can send IP packets to any other site in the same VPN.
Each VPN is associated with one or more VPN routing or forwarding instances (VRFs). A VRF consists of an IP routing table, a derived Cisco express forwarding (CEF) table, and a set of interfaces that use this forwarding table.
The router maintains a separate routing and CEF table for each VRF. This prevents information being sent outside the VPN and allows the same subnet to be used in several VPNs without causing duplicate IP address problems.
The router using Multiprotocol BGP (MP-BGP) distributes the VPN routing information using the MP-BGP extended communities.
For more information regarding the propagation of updates through a VPN, see the following URLs:
VPN Route Target Communities
BGP Distribution of VPN Routing Information
MPLS Forwarding
Conventions
The letters below represent the different types of routers and switches used.
P : Provider's core router
PE : Provider's edge router
CE : Customer's edge router
C : Customer's router
This diagram shows a typical configuration illustrating the conventions outlined above.
Hardware and Software Versions
This configuration was developed and tested using the software and hardware versions shown below.
P and PE routers:
Software - Cisco IOS?Software Release 12.1(3)T. Release 12.0(5)T includes the MPLS VPN feature.
Hardware - Any Cisco router from the 3600 series or higher, such as the Cisco 3660 or 7206.
C and CE routers: You can use any router that can exchange routing information with its PE router.
Network Diagram
Configuration Procedures
Enabling ip cef
Make sure that ip cef is enabled. For improved performance, use ip cef distributed (where available). Complete the following steps on the PEs after MPLS has been set up (configuring tag-switching ip on the interfaces).
Create one VRF for each VPN connected using the ip vrf
Specify the correct route distinguisher used for that VPN. This is used to extend the IP address so that you can identify which VPN it belongs to.
rd
Set up the import and export properties for the MP-BGP extended communities. These are used for filtering the import and export process.
route-target [export|import|both]
Configure the forwarding details for the respective interfaces using the following command.
ip vrf forwarding
Remember to set up the IP address after doing this.
Depending on the PE-CE routing protocol you are using, you can configure static routes or routing protocols (RIP, Open Shortest Path First [OSPF], or BGP) between PE and CE. Detailed configurations are available on the MPLS over ATM Support Page.
Configuring MP-BGP
Configure MP-BGP between the PE routers. There are several ways to configure BGP, such as using the route reflector or confederation methods. The method used here梔irect neighbor configuration梚s the simplest and the least scalable.
Declare the different neighbors.
Enter the address-family ipv4 vrf
Redistribute the static routing, RIP, or OSPF information.
Redistribute connected routing information.
Activate BGP neighboring with the CE routers.
Enter the address-family vpnv4 mode, and complete the following steps:
Activate the neighbors.
Specify that extended community must be used. This is mandatory.
Configurations
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