In this post, we are going to go through the implementation and verification steps of Inter-AS Option B (defined in RFC4364 http://tools.ietf.org/html/rfc4364#page-32 ). Please refer to previous post Inter-AS Options to for the definitions, and differences of the three.
In option B implementation, ASBRs themselves are PE routers. They learn VPN-IPv4 routes from other PEs from the same AS via MP-iBGP (either directly or via Route Reflectors). The ASBR from one AS then have an eBGP session(s) with other AS ASBR to redistribute the VPN-IPv4 routes to the other AS. The later ASBR then redistributes those VPN-IPv4 labeled routes to the rest of the PEs belonging to that AS.
In this topology, we use Cisco IOS routers (R1 – R3) in AS100, as well as Juniper routers (R4 – R6) in AS200, just for demonstration of configuration and verification on both platforms. Typically for connectivity beween ASes, one eBGP…
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