http://www.rfc-editor.org/rfc/rfc1063.txt
RFC 1063: IP MTU discovery options, J.C. Mogul, C.A. Kent, C. Partridge, K. McCloghrie1988-07-01T23:00:00-00:00A pair of IP options that can be used to learn the minimum MTU of a path through an internet is described, along with its possible uses. This is a proposal for an Experimental protocol.