jim@tiamat.fsc.com (Jim O'Connor) (08/18/90)
Were's the situation: We have an HP 9000/835 running HP-UX 7.0, an Annex II terminal server, and a few 386PC's running SCO Xenix with TCP/IP from SCO. If we do rlogins such as: Client Server -------- ------------ Annex II HP 835 Xenix Xenix Xenix HP 835 and the client end of the connection crashes (only one of the 386's is on a UPS, and none of the Annex terminal servers are), the server end of the connection NEVER goes away, unless the processes are killed by hand or the server machine is rebooted. Is this the "normal" behavior, or am I missing something completely obvious? Thanks for any help. ------------- James B. O'Connor jim@tiamat.fsc.com Ahlstrom Filtration, Inc. 615/821-4022 x. 651
08071TCP%MSU@PUCC.PRINCETON.EDU (Doug Nelson) (08/21/90)
>Were's the situation: We have an HP 9000/835 running HP-UX 7.0, an Annex II >terminal server, and a few 386PC's running SCO Xenix with TCP/IP from SCO. >If we do rlogins such as: [list omitted] >and the client end of the connection crashes [...], the server end of the >connection NEVER goes away, unless the processes are killed by hand or the >server machine is rebooted. > >Is this the "normal" behavior, or am I missing something completely obvious? This is "normal" behavior for TCP connections. There is no mechanism in the TCP protocol spec for detecting a broken connection, unless the working end attempts to send more data across the connection. That will eventually trigger a timeout, or, if the other host has been restarted, it will send a reset, immediately closing the connection. Many Unix systems (most BSD-based systems) have a mechanism called "keep-alive" built into the TCP code. A periodic probing of the connection is done to see if it is still alive. The probe is a single data byte just outside the valid data window; on a good connection, this triggers an ACK packet in response. If the connection is gone, a reset will be sent in response. The keep-alive can have a negative effect, however, in cases where both end systems are still alive, but the network is temporarily disrupted due to a network problem of some sort. Doug Nelson Michigan State University