routing protocols will provide path-MTU

Craig Partridge <craig@NNSC.NSF.NET> Mon, 26 February 1990 12:43 UTC

Received: from decwrl.dec.com by acetes.pa.dec.com (5.54.5/4.7.34) id AA28744; Mon, 26 Feb 90 04:43:51 PST
Received: by decwrl.dec.com; id AA03097; Mon, 26 Feb 90 04:43:46 -0800
Message-Id: <9002261243.AA03097@decwrl.dec.com>
To: deering@pescadero.stanford.edu
Cc: mtudwg
Subject: routing protocols will provide path-MTU
Date: Mon, 26 Feb 90 07:42:59 -0500
From: Craig Partridge <craig@NNSC.NSF.NET>

> This keeps popping up.  Would someone please explain this in more
> detail?  Exactly how are the routing protocols going to maintain or
> acquire the path-MTU information that hosts need, and how are the hosts
> going to learn that information and detect changes in that information?
> I can imagine several possible schemes, including giving up dynamic,
> datagram routing in favor of static, virtual-circuit routing (which
> seems to be where politics-based routing is headed), but I'd really
> like to get some facts before I start flaming. :-)

Steve:

    I don't know for sure, but my limited understanding was that with
full topology information (ala ARPANET SPF), a router could figure out
the safe MTU between two points, and could notify a host if too large
a datagram came past.

    HOWEVER, the advent of hiding area information (IS-IS and OSPF) may
mean that it is no longer possible to a router to derive the optimal MTU
for a path.  (Mind you, the area could advertise the lowest MTU of any
through path within it, but that clearly leads to very non-optimal
situations).

    <Now, Noel can tell me I'm all wet>

Craig