What are two reasons why all IBGP routers in a single AS must be in a full mesh topology? (Choose two.)
- IBGP routing requires fault tolerance provided by fully meshed connections.
- Transit traffic is not allowed within the AS where IBGP is used.
- An IBGP router does not prepend the ASN to the AS_Path attribute.
- An IGP provides fast convergence among IBGP routers.
- An IBGP router does not advertise an NLRI received from one IBGP peer to another IBGP peer.
Explanation: IBGP peers do not prepend their ASN to AS_Path because the NLRI would fail the validity check and would not install the prefix into the IP routing table. No other method exists for detecting loops with IBGP sessions and RFC 4271 prohibits the advertisement of an NLRI received from an IBGP peer to another IBGP peer. RFC 4271 states that all BGP routers in a single AS must be fully meshed to provide a complete loop-free routing table and prevent traffic from being dropped.
Exam with this question: CCNP Enterprise: Advanced Routing (Version 8.0) – BGP Exam
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