Name: Cisco NCS 540 Series
Brand: Cisco
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Figure 2: eBGP Connection Between Two Subautonomous Systems in a Confederation

In this confederation configuration:

• CEBGP border edge routers function as neighboring peers between the subautonomous systems. The

subautonomous systems use eBGP to exchange route information.

• Each CEBGP border edge router (CEBGP-1 and CEBGP-2) assigns a label for the router before distributing

the route to the next subautonomous system. The CEBGP border edge router distributes the route as a

VPN-IPv4 address by using the multiprotocol extensions of BGP. The label and the VPN identifier are

encoded as part of the NLRI.

• Each PE and CEBGP border edge router assigns its own label to each VPN-IPv4 address prefix before

redistributing the routes. The CEBGP border edge routers exchange IPV-IPv4 addresses with the labels.

The next-hop-self address is included in the label (as the value of the eBGP next-hop attribute). Within

the subautonomous systems, the CEBGP border edge router address is distributed throughout the iBGP

neighbors, and the two CEBGP border edge routers are known to both confederations.

MPLS VPN Inter-AS BGP Label Distribution

This section is not applicable to Inter-AS over IP tunnels.

Note

You can set up the MPLS VPN Inter-AS network so that the ASBRs exchange IPv4 routes with MPLS labels

of the provider edge (PE) routers. Route reflectors (RRs) exchange VPN-IPv4 routes by using multihop,

multiprotocol external Border Gateway Protocol (eBGP). This method of configuring the Inter-AS system is

often called MPLS VPN Inter-AS BGP Label Distribution.

Configuring the Inter-AS system so that the ASBRs exchange the IPv4 routes and MPLS labels has the

following benefits:

• Saves the ASBRs from having to store all the VPN-IPv4 routes. Using the route reflectors to store the

VPN-IPv4 routes and forward them to the PE routers results in improved scalability compared with

configurations in which the ASBR holds all the VPN-IPv4 routes and forwards the routes based on

VPN-IPv4 labels.

L3VPN Configuration Guide for Cisco NCS 540 Series Routers, IOS XR Release 6.3.x

MPLS L3VPN Overview

MPLS VPN Inter-AS BGP Label Distribution

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Cisco NCS 540 Series Specifications

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