In the topology, I have all internal Peers (Site A,B,C) in AS 65002. these peers are connected through the transit ATT router (using AS number 1500 as in topology). The problem is, site C can ping only to the advertised networks from site A ( and site B( It doesn't see the network segment between site A and site B i.e. the 10.10.254.x network even thou these are all being advertised. However, the ATT router could see it with no issues.

What am I missing?enter image description here

  • Could you include the BGP configs of all three routers?
    – HAL
    Commented Mar 13, 2015 at 15:03

2 Answers 2


ATT router will advertise the route to router C, but the path will contain AS 65002 (from A).
C will see that as a routing loop (since its AS is also 65002) and discard the route.

If you can, change the AS number of C to something else.

  • if I wanted to have the same AS number 65002 can you suggest a way to do it? Commented Mar 13, 2015 at 15:06
  • I can think of ways to jury-rig a way to do it, but I wouldn't recommend any of them. The best way is to use a different AS.
    – Ron Trunk
    Commented Mar 13, 2015 at 15:10
  • Great! You can mark the question answered if it helped you.
    – Ron Trunk
    Commented Mar 13, 2015 at 15:12

Another method is use L3vpn via bgp option A technique at ATT router with igp protocols at both ends and redistribute into address-family ipv4 vrf Cust_A under bgp 1500. it works properlyand it overcome AS loop prevention feature. Also you can use lable swaping per route like as seemless vpn technique

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