Mpls Vpn Inter-As Bgp Label Distribution - Cisco NCS 540 Series Configuration Manual

MPLS VPN Inter-AS BGP Label Distribution

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
• Each CEBGP border edge router (CEBGP-1 and CEBGP-2) assigns a label for the router before distributing
• Each PE and CEBGP border edge router assigns its own label to each VPN-IPv4 address prefix before
MPLS VPN Inter-AS BGP Label Distribution
Note
This section is not applicable to Inter-AS over IP tunnels.
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
L3VPN Configuration Guide for Cisco NCS 540 Series Routers, IOS XR Release 6.3.x
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subautonomous systems use eBGP to exchange route information.
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.
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.
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.
MPLS L3VPN Overview