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How do I configure Inter AS option A for back-to-back VRF connectivity?

Can anyone please provide me with a sample configuration and topology for back to back VRFs ( Inter-AS option A )?

Basically, I am looking how to configure these two ASBRs (R3 and R4) with Inter-As option A in the above topology. The iBGP peering has already been done. The only thing I am left with to start is the eBGP peering.

  • Why do you want to do option A?
    – Ron Trunk
    May 7, 2016 at 14:15
  • Yes. I want to configure inter as option a May 7, 2016 at 16:13
  • But why option A?
    – Ron Trunk
    May 7, 2016 at 16:13
  • Not exaclty, this is just for learning purpose. Are there any drawbacks with using option A ? Why shouldn't i use option A ? May 7, 2016 at 16:25
  • I was trying to understand your requirements. Generally, option A doesn't scale very well. Do you have your two MPLS networks already set up?
    – Ron Trunk
    May 7, 2016 at 16:32

1 Answer 1


This is only a partial config, as I assume you already have BGP running on the PE routers, and the interfaces are in the correct vrf. Each ASBR treats the other as a CE router:

router bgp 100
address-family ipv4 vrf AS-200
neighbor a.b.c.d remote-as 200
neighbor a.b.c.d activate

Do the same for AS 200

  • This was the exact thing i was looking for. It worked. Thanks alot !! May 7, 2016 at 18:04

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