Path: utzoo!utgpu!water!watmath!clyde!att!ihnp4!amdcad!phil
From: phil@amdcad.AMD.COM (Phil Ngai)
Newsgroups: comp.dcom.lans
Subject: Re: Can Ethernet TCP/IP lock up?
Message-ID: <21695@amdcad.AMD.COM>
Date: 20 May 88 17:59:17 GMT
References: <299@fedeva.UUCP> <21674@amdcad.AMD.COM> <21680@amdcad.AMD.COM> <10303@ulysses.homer.nj.att.com>
Reply-To: phil@amdcad.UUCP (Phil Ngai)
Organization: Advanced Micro Devices
Lines: 28

In article <10303@ulysses.homer.nj.att.com> smb@ulysses.homer.nj.att.com (Steven Bellovin) writes:
>There is in general *no way to
>know* if a jabber-detect has failed -- there is no standard diagnostic
>for it!  Thus, the second failure (of a controller) can happen at any
>time in the future; the two don't have to be coincident.

This is a very important principle. I call it the "testing your
spare tire" policy. Redundancy without an alarm to notify you
when it has been invoked is very dangerous.

I tend to think of things like this as belonging under network
management.

The designers of Ethernet were concerned about this. That is why
the version 2 has the "heartbeat" or collision presence test
at the end of every packet.

Unfortunately jabber detect is not automated like this. There are
transceiver testers that can be used for this. Either Cabletron
or Titn made one that had such a test, unfortunately I looked
at this two years ago and don't remember which one. In any case,
you'd have to manually go out and hook up the transceiver tester
to check the jabber detect.
-- 
Make Japan the 51st state!

I speak for myself, not the company.
Phil Ngai, {ucbvax,decwrl,allegra}!amdcad!phil or phil@amd.com