Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!usc!zaphod.mps.ohio-state.edu!sunybcs!boulder!daemon
From: jerry@OLIVEY.ATC.OLIVETTI.COM (Jerry Aguirre)
Newsgroups: comp.dcom.sys.cisco
Subject: KeepAlives and half duplex failures
Message-ID: <19499@boulder.Colorado.EDU>
Date: 10 Apr 90 10:29:41 GMT
Sender: daemon@boulder.Colorado.EDU
Lines: 20

Let me preface this by stating that this is a request for information
and I don't know this to be a problem but....

It seems to me that keepalives do exactly the wrong thing when one half
of a line fails.  Given that most lines are full duplex it is quite
reasonable for one direction to fail while the other continues to
operate.

Assume that the line from A to B is working but the reverse direction
has a problem.  B will continue to receive keepalives and, worse,
routing information from A.  But when it tries to use that line to B the
packet gets dropped on the floor.  Meanwhile A has a potentially good
path to B but won't use it for lack of keepalives and routing updates.

I think I observed this happening while debugging a line.  Is this how
it really works or are keepalives smarter than that?  Does the keepalive
packet contain information about whether the sender has been receiving
keepalives on that line?

					Jerry Aguirre