MTU Extended Community for BGP4 draftzengidrbgpmtuextension00 Q Zeng

MTU Extended Community for BGP-4 draft-zeng-idr-bgp-mtu-extension-00 Q. Zeng, J. Dong (Huawei Technologies) IETF 81 IDR July 2011 Quebec 1

Background • Path MTU Discovery: RFC 1191, RFC 1981 • LDP MTU Discovery: RFC 3988 – To make path MTU discovery work properly in MPLS network • There is a gap in MTU discovery in MPLS network – An example, Inter-AS IP VPN, Option C AS 1 label mapping AS 2 labeled /32 route 2. 2 1. 1 P 1 CE 1 PE 1 MP-IBGP LDP MTU discovery ASBR 1 ASBR 2 MP-EBGP ? P 2 PE 2 CE 2 MP-IBGP LDP MTU discovery 2

Solution • BGP LSP Path MTU: – Path MTU of the LSP from a given BGP LSR to a specific prefix • BGP LSR Link MTU: – Minimum MTU between a given BGP LSR and its downstream BGP LSR • A new BGP extended community – MTU extended community 3

Solution (Cont. ) • Signaling procedures labeled /32 route with MTU ext community 2. 2 1. 1 P 1 CE 1 PE 1 AS 1 LDP MTU discovery ASBR 1 ASBR 2 BGP MTU discovery P 2 PE 2 CE 2 AS 2 LDP MTU discovery BGP MTU discovery • Avoid unnecessary flapping – If the BGP LSP Path MTU decreases, a new update SHOULD be advertised immediately; – if the BGP LSP Path MTU increases, the speaker MAY hold down the update. 4

Next Steps • Solicit comments & feedbacks 5