Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ames!oliveb!mintaka!daemon
From: jtw@lcs.mit.edu (John Wroclawski)
Newsgroups: comp.protocols.appletalk
Subject: Re: IP fragmentation (was SMTP mail to Mac's)
Message-ID: <JTW.89Sep12212000@mercury.lcs.mit.edu>
Date: 13 Sep 89 01:21:49 GMT
References: <473@shuldig.Huji.Ac.IL>
	<1989Sep5.121104.10155@gpu.utcs.utoronto.ca> <37995@bu-cs.BU.EDU>
Sender: daemon@mintaka.lcs.mit.edu (Lucifer Maleficius)
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In-reply-to: budd@bu-cs.BU.EDU's message of 12 Sep 89 20:39:24 GMT

In article <37995@bu-cs.BU.EDU> budd@bu-cs.BU.EDU (Philip Budne) writes:

   From: budd@bu-cs.BU.EDU (Philip Budne)
   Summary: MacTCP sends bad MSS for localtalk?

   In article <1989Sep5.121104.10155@gpu.utcs.utoronto.ca>
	   nishri@gpu.utcs.UUCP (Alex Nishri) writes:

   >The first problem is that the Mac II must be directly on an ethernet
   >and not on a Localtalk behind a Gatorbox.  This is because the
   >Gatorbox (and Fastpath, we understand) do not handle TCP/IP packet
   >fragmentation; most Internet SMTP servers use large packet sizes and
   >these end up on the floor.

   I seem to remember NCSA Telnet over localtalk sends a TCP MSS option
   requesting minimal (576) maximum segment size.  The one MacTCP
   application I looked at sends an MSS request of 1024 when running over
   localtalk.

Actually, Gatorboxes are supposed to fragment IP packets correctly.
(Please let Cayman know if you think otherwise...). Most older Mac IP
implementations don't do reassembly, though.

IMHO it would still be better if MacTCP requested a small enough MSS
to avoid fragmentation. Aside from not working with some current
Ethernet-Localtalk gateways, I suspect that some host hardware can't
handle the back-to-back packets and will often drop the second
fragment.