Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!nrl-cmf!ames!pasteur!ucbvax!decwrl!sun!pitstop!sundc!seismo!uunet!mcvax!cernvax!jmg
From: jmg@cernvax.UUCP (jmg)
Newsgroups: comp.dcom.lans
Subject: Re: Problems finding forwarding tables on LAN Bridges
Keywords: bridge
Message-ID: <921@cernvax.UUCP>
Date: 30 Jan 89 07:50:20 GMT
References: <917@cernvax.UUCP> <13701@bellcore.bellcore.com>
Reply-To: jmg@cernvax.UUCP ()
Organization: CERN European Laboratory for Particle Physics, CH-1211 Geneva, Switzerland
Lines: 37

In article <13701@bellcore.bellcore.com> karn@ka9q.bellcore.com (Phil Karn) writes:
>
>Yes, I've already done this here at Bellcore. I wrote a program called
>"locate" that, given an ethernet address, reads a topology file and queries
>the Lan Bridge 100s to find the segment containing that address.

Would be nice to know what is in the topology file. However, my point
was rather that I do not necessarily know all the Ethernet addresses
in use. I know one could probably create such a list, but it would be
long.

>The algorithm works by a simple process of elimination. You start with a
>complete list of your cable segments, and you search each bridge's
>forwarding table in turn for the target address. (I do this in parallel,
>since the RBMS protocols are rather slow.) When a bridge replies that the
>desired address is on port A, you can rule out the segment attached to port
>B.  Eventually you (hopefully) end up with one segment.

I assume this means that either the topology file includes the A and B
side information or you have a standard way of knowing which side is which.
I also suppose that you could automatically run this procedure from a list
of Ethernet addresses: how long would it take if the list is around 1000?
Also, what happens if some bridges have forgotten the address while
others still remember it? Finally, what about bridges different from
LANBridge 100?

>The process is not 100% reliable, but it works well enough to be useful.  I
>guess I'll ask about getting it released.

It would certainly be useful in an emergency situation where you want to
know the segment of some enmerdeur (Franglais: you can guess what it means!).
However, it was not really what I was after.
-- 
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| | | | |_)  /_)     |  __/_) | (___\ | (_/ |  J. M. Gerard, Div. DD, CERN,
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