Credit where credit is due

mogul (Jeffrey Mogul) Mon, 16 April 1990 18:59 UTC

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From: mogul (Jeffrey Mogul)
Message-Id: <>
Date: 16 Apr 1990 1059-PST (Monday)
To: mtudwg
Subject: Credit where credit is due

In the process of editing Steve's draft proposal, I went through
the material I used 2 years ago when writing "Fragmentation Considered
Harmful", and found this message:
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    Subject: Re: IP Datagram sizes
    I like the idea of an IP-level solution to the fragmentation problem
    since it has application to UDP protocols (I know that none that exist
    today could use it, but that's no excuse for ignoring UDP).
    Isn't there a destination unreachable message with the reason being
    "can't fragment and had to" (sorry my ICMP spec is at the office)?  If
    not, we could certainly add one.
    In that case, the idea is to always send TCP packets with the "don't
    fragment" bit set.  Use the scheme suggested that keeps track of MTU's
    in the routing cache.  Update the cache based on DU's received
    (decrease the MTU a bit and try again) -- time out the entry on a long
    timer to be able to detect new routes.
    The obvious improvement is to have the ICMP message also include the
    MTU restriction that is appropriate -- that requires changing ICMP, of
    course, but it would probably be a good idea.