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