Path: utzoo!utgpu!watmath!clyde!att!ucbvax!RADC-MULTICS.ARPA!Ata
From: Ata@RADC-MULTICS.ARPA ("John G. Ata")
Newsgroups: comp.protocols.tcp-ip
Subject: Re: Mail Delivery Problems
Message-ID: <881129163302.072044@RADC-MULTICS.ARPA>
Date: 29 Nov 88 16:33:00 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 20


We have had problems sending to BSD4.2 and ULTRIX systems.  In our case
a packet gets sent but never acknowledged.  Subsequent retrasmissions
are fruitless and the connection eventually times out.  An analysis of
the packets that are affected show that only certain size packets have
difficulty.  Not counting the TCP or IP headers, a packet with a data
field of 15, 33, 51 ...  is affected (every 18 octets).  A look at a 4.2
BSD system showed that the IP layer was throwing the packets away
because the size field in the IP header wasn't the same size that the
device interface (X.25) thought it was.  You can see this with the
"netstat -s" command line.  Because we can talk with other systems
(including BSD 4.3) with no problem, I don't suspect our IP putting an
incorrect size field.
          Sending data via TELNET doesn't cause any problems because
most TELNETs are 1 octet/packet so the problem doesn't occur.  We can
duplicate this problem is line mode, however, where the packet size will
be the line size.
          Hope this helps...

                              John G. Ata