Proper functioning of path Maximum Transmission Unit (MTU) discovery
[RFC1191] requires that IP routers have knowledge of the MTU for each
link to which they are connected. As MPLS progresses, [RFC3988]
specifies extensions to LDP in support of LDP LSP MTU discovery. For
the LSP created using Border Gateway Protocol (BGP) [RFC3107], it
does not have the ability to signal the path MTU to the ingress Label
Switching Router (LSR). In the absence of this functionality, the
MTU for the BGP LSP must be statically configured by network
operators or by equivalent off-line mechanisms.
This document defines the MTU Extended Community for BGP in support
of BGP LSP MTU discovery.