Nov 19 2008

Inter-AS MPLS VPN Option b – Type 2a

Inter AS MPLS VPN Option b has three options as described below.

In the first option ie 2a an MP-eBGP session is configured between ASBRs to exchange VPNv4 prefixes.

The Link between the ASBRs does NOT run LDP/TDP and does not require an IGP.

The link is a straight forward point to point IP link.

A sample topology can be seen below.

In the first option for prefixes advertised from CE1 a VPN label will be generated at 3 points.

1-At PE1 a Label will be allocated for the customer prefix.

2-At PE2 the VPN label will be changed as PE2 will advertise the customer prefix with a new next hop.

3-At PE3 the VPN label will be changed as PE3 will have “next-hop-self” configured on its session with PE4.

To can see the VPN label generated as an “in” label using the commands

sh ip bgp vpnv4 all label

On PE1, ASBR1 and ASBR2 you will see the locally generated “in” label.