Why is interface loopback 0 of R4 missing in the BGP table of R2?

Refer to the exhibit. Why is interface loopback 0 of R4 missing in the BGP table of R2?

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A. R2 is not configured as a route reflector client.
B. The route is originating in the same cluster list.
C. The route originated within the same AS.
D. The next hop is not reachable form R2.

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2 thoughts on “Why is interface loopback 0 of R4 missing in the BGP table of R2?

  1. C is correct – had to lab it out.

    We see “bgp cluster id 3.3.3.3” configured on the router R2, it’s the root cause of 4.4.4.4 not appearing on R2.

    As per BGP route reflector RFC, Route reflectors append Cluster ID of their own before propagating routes further.
    Since R3 is not explicitly configured with a Cluster ID, it will assume it’s cluster ID from it’s router ID, which is 3.3.3.3 on loopback 0 and then will reflect the 4.4.4.4 route with it’s cluster ID of 3.3.3.3.

    R2 will not accept that route from reflector due to “bgp cluster id 3.3.3.3” configured and the route update is also tagged with cluster ID of 3.3.3.3. Loop prevention of route reflection mechanism is not to accept routes with it’s own Cluster IDs.

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