Xref: utzoo comp.sys.mac.comm:3034 comp.protocols.tcp-ip:15424
Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!usc!cs.utexas.edu!uunet!maverick.ksu.ksu.edu!hoss!sardion!mosemann
From: mosemann@sardion.unl.edu (Russell Mosemann)
Newsgroups: comp.sys.mac.comm,comp.protocols.tcp-ip
Subject: Re: MacTCP has bad segment size
Keywords: MacTCP maximum segment size error
Message-ID: <1991Mar27.144104.179@hoss.unl.edu>
Date: 27 Mar 91 14:41:04 GMT
References: <1991Mar26.213034.8544@hoss.unl.edu>
Sender: news@hoss.unl.edu (Network News Administer)
Reply-To: mosemann@unl.edu
Distribution: na
Organization: University of Nebraska - Lincoln
Lines: 40

In <1991Mar26.213034.8544@hoss.unl.edu> mosemann@sardion.unl.edu (Russell Mosemann) writes:

>   Weeks and weeks ago, people were discussing the problem MacTCP has
>with determining the MSS (maximum segment size).  I read the messages
>but never wrote anything down or saved it because we didn't have that
>problem before.
[...]
>   I dug into the packets and found that it was requesting a window size
>of *10241*.  Could someone mail the fix for this (I think it was done by
>Steve Dorner)?
[...]

   OK.  I got the fix, but it didn't solve the problem.  Now for a
little more information.  I'm using MacTCP 1.0, MacPOP 1.5.7, Systems
6.0.5 and 6.0.7, and Ethernet'ed and LocalTalk'ed Macs (SE/30, SE, and
Classic).
   MacPOP tries to establish the tcp connection.  I see the 4 or so
packets go to the POP host, but there is no return response.  Our
sniffer reports:

Ethernet:  ( router -> pop host)  type: IP(0x0800)
Internet:    Mac IP -> pop host IP  hl: 6  ver: 4  tos: 0
 len: 48  id: 0x0009  fragoff: 0  flags: 00  ttl: 58  prot: TCP(6)
 xsum: 0x6a75 bsec resv 4:
TCP:  10593 -> POP-2(109)  seq: 5d60a560  ack: ----
 win: 11648  hl: 6  xsum: 0x3a3a  urg: 0  flags: <SYN>  mss: 576

   Only the Ethernet and IP addresses have been changed.  This is
from a Mac Classic going through a FastPath 4 running version 8.x of
KSTAR.
   I can telnet to the port and issue commands by hand with no problem.
The mss doesn't seem to be the problem that I thought it was.  The
window size seems a little strange, but maybe it's OK, too.  The thing I
have never seen in a TCP packet before is the "bsec resv 4:".  Does
anything look wrong in this packet?  Thanks.
--
Russell Mosemann                  Internet:             mosemann@unl.edu
Network Analyst                   Bitnet:               mosemann@unlvax1
Computing Resource Center         UUCP:   ..!uunet!hoss.unl.edu!mosemann
University of Nebraska - Lincoln  Voice:  (402) 472-5930   Fax: 472-5280