Path: utzoo!news-server.csri.toronto.edu!rutgers!dimacs.rutgers.edu!seismo!ukma!rex!wuarchive!m.cs.uiuc.edu!roundup.crhc.uiuc.edu!ux1.cso.uiuc.edu!resnick
From: resnick@cogsci.uiuc.edu (Pete Resnick)
Newsgroups: comp.sys.mac.comm
Subject: Re: MacTCP and Cabletron E6000
Keywords: mac,ethernet,tcp
Message-ID: <1991Mar15.004519.28684@ux1.cso.uiuc.edu>
Date: 15 Mar 91 00:45:19 GMT
References: <pst.668988866@dschub>
Sender: usenet@ux1.cso.uiuc.edu (News)
Distribution: usa
Organization: University of Illinois at Urbana
Lines: 32


When an TCP connection hangs when sending large amounts of data using
MacTCP on an Ethernet card, chances are it is one of those Ethernet
cards that mishandles the maximum segment size (MSS). MSS is a number
that MacTCP communicates to the remote host to tell it how big a piece
of data can be sent. Some Ethernet cards (e.g. some Cabletron and Dove
cards) are not communicating it correctly to MacTCP. There is a fix:

In MacTCP 1.0, MacTCP did not figure out the MSS correctly for DDP-IP
gateways, so Steve Dorner here at UIUC came up with a fix. This same
fix still works on the newer versions of MacTCP and fixes the problem
for Ethernet card. It seems to just tell MacTCP not to advertise any
MSS to the remote host, which leaves it at a reasonable default. The
fix is peformed with ResEdit as follows:

1. Open the MacTCP file with ResEdit.
2. Open the DRVR resources picker.
3. Open the one DRVR resource that is there. In older version of ResEdit,
   you must use the "Open General" choice.
4. Find the hexadecimal string "337c02040014" and change it to read
   "337c01010014".
5. Save and close the file.

Now MacTCP should work properly.

pr
--
Pete Resnick             (...so what is a mojo, and why would one be rising?)
Graduate assistant - Philosophy Department, Gregory Hall, UIUC
System manager - Cognitive Science Group, Beckman Institute, UIUC
Internet/ARPAnet/EDUnet  : resnick@cogsci.uiuc.edu
BITNET (if no other way) : FREE0285@UIUCVMD