Mpls Vpn Inter-As Bgp Label Distribution; Exchanging Ipv4 Routes With Mpls Labels - Cisco CRS Configuration Manual

MPLS VPN Inter-AS BGP Label Distribution

• Each PE and CEBGP border edge router assigns its own label to each VPN-IPv4 address prefix before
• For more information about how to configure confederations, see the .
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
• Having the route reflectors hold the VPN-IPv4 routes also simplifies the configuration at the border of
• Enables a non-VPN core network to act as a transit network for VPN traffic. You can transport IPv4
• Eliminates the need for any other label distribution protocol between adjacent label switch routers (LSRs).

Exchanging IPv4 Routes with MPLS labels

This section is not applicable to Inter-AS over IP tunnels.
Note
You can set up a VPN service provider network to exchange IPv4 routes with MPLS labels. You can configure
the VPN service provider network as follows:
• Route reflectors exchange VPN-IPv4 routes by using multihop, multiprotocol eBGP. This configuration
Cisco IOS XR Virtual Private Network Configuration Guide for the Cisco CRS Router, Release 6.1.x
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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.
the network.
routes with MPLS labels over a non-MPLS VPN service provider.
If two adjacent LSRs are also BGP peers, BGP can handle the distribution of the MPLS labels. No other
label distribution protocol is needed between the two LSRs.
also preserves the next-hop information and the VPN labels across the autonomous systems.
Implementing MPLS Layer 3 VPNs