What is the potential problem?

A network administrator notices that the BGP state drops and logs are generated formissing BGP hello keepalives.

What is the potential problem?
A . Incorrect neighbor options
B . Hello timer mismatch
C . BGP path MTU enabled
D . MTU mismatch

View Answer

Answer: D

Explanation:

BGP neighbors form; however, at the time of prefix exchange, the BGP state drops and the logs generate missing BGP hello keepalives or the other peer terminates the session.

Here are some possible causes:

*The interface MTU on both routers do not match.

*The interface MTU on both routers match, but the Layer 2 domain over which the BGP session is formed does not match.

*Path MTU discovery determined the incorrect max datasize for the TCP BGP session.

*The BGP Path Maximum Transmission Unit Discovery (PMTUD) could be failing due to PMTUD ICMP packets blocked (firewal or ACL)

http://www.cisco.com/c/en/us/support/docs/ip/border-gateway-protocol-bgp/116377-troubleshoot-bgp-mtu.html