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From: jbvb@VAX.FTP.COM (James Van Bokkelen)
Newsgroups: comp.protocols.tcp-ip.ibmpc
Subject: Re: ARCnet packet driver
Message-ID: <8910301436.AA14375@vax.ftp.com>
Date: 30 Oct 89 14:36:59 GMT
References: <1989Oct27.195255.5486@sun.soe.clarkson.edu>
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
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The reason you don't want to try to hide the fact that it's ARCNet by
pretending to be Ethernet (class 1) is the difference in MTUs: If you are
faking Ethernet, lots of software will try to send 1514-byte packets, and
almost everything will try to send 1080 or so.  This will come up against
the 508-byte ARCNet limit and the application will go down in flames...

The get_parameters() function in v1.09 of the Packet Driver spec does
let an application see the MTU, but there are lots of applications out
there which don't check (or don't expect it to change).  I suppose you
could look at the out-going IP datagram and fragment it, but that
would cause troubles at other levels.  I definitely wouldn't go so far
as to hack on the TCP MSS option in SYN packets (ugh, shudder, retch...).

jbvb