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
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
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