Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!ucbvax!PURDUE.EDU!narten
From: narten@PURDUE.EDU (Thomas Narten)
Newsgroups: comp.protocols.tcp-ip
Subject: Re: Re-fragmenting IP Datagrams
Message-ID: <8902231455.AA04706@percival.cs.purdue.edu>
Date: 23 Feb 89 14:55:41 GMT
References: <8902230119.AA22877@flora.wustl.edu>
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
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>I believe the specifications also require all networks to be able to
>forward a 576 octet datagram without fragmentation.

576 is not a lower limit on the size of a datagram fragment, but an
upper limit on what a destination is *required* to accept.  The
sender/destination might agree to exchange larger datagrams, but any
such agreements are private to the communicating end points.

From RFC-791:

    Every internet module must be able to forward a datagram of 68
    octets without further fragmentation.  This is because an internet
    header may be up to 60 octets, and the minimum fragment is 8 octets.

    Every internet destination must be able to receive a datagram of 576
    octets either in one piece or in fragments to be reassembled.

Thomas