From: rick@sadtler.sadtler.com (Rick Morris)
Subject: Bridge or Router SUMMARY
Organization: Sadtler Research Laboratories
Date: Wed, 9 Sep 1992 12:34:13 GMT

Hello all.

A couple of weeks back I asked about bridges and routers,
and what to do about a Novell/TCP thinnet backbone.
At times, the NFS on the TCP side would hang up for long
periods of time.  The receive light on a repeater would indicate
constant activity on the PC/Novell side at these times.  Upon
investigation, we find that the PC/Novell receive light is on
during some big PC Database queries.  At the time of my cry for
help, a series of particularly long queries were being generated.

I received many real good responses, my thanks to everyone!
I summarize below.

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1.  Differences between a Bridge and Router

(Taken from Rodney Campbell (rodney@cssc-syd.tansu.com.au)'s response):

In simple terms there are a number of network devices which work at
different levels (of the OSI model).

A Repeater is a device that works at OSI Level 1 - The Physical layer. It
simply repeats the waveforms on one side to the other. It knows nothing
about higher level protocols.

A Bridge is a device that works at OSI Level 2 - The Link layer. It can
filter traffic based on MAC level addresses (Ethernet Addresses) - These
bridges are usually learning bridges which learn where devices are over a
period of time and then discard the information after a while because it
is possible for you to move stuff around (The purge time is usually in the
order of minutes). A bridge does not understand higher level protocols
like IP or IPX etc. It just repeats frames like HDLC etc.

A Router is a device that works at OSI Level 3 - The Network layer. It can
understand routing information and simply routes packets to another
network based on Network Level Addresses (The IP Address is one of these).
A router must understand the protocol it has to route (IP, IPX, AppleTalk,
etc).

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2.  Recommendations for my situation:

(Taken from Stephane Bortzmeyer (bortzmeyer@cnam.cnam.fr)'s response):

If the problem lays in the limitations of thin-net, a bridge is sufficient
(because you have a layer 2 problem). It will not slow down your network,
since all the bridges are as fast as Ethernet itself.
If you have other problems (security and need for "clever" filtering,
different IP networks on one cable, etc), you need a router.

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3.  Could be hardware...

(Taken from Gary Heston (gary@sci34hub.sci.com)'s response):

So, how long is this backbone? Thin is limited to 185 meters (about
606 feet). It doesn't sound like you're exceeding the connection
limit (30).

...

So, did you swap the ports on the repeater and verify that the 
indications are the same? Cabletron has a good reputation, but
everything breaks sometime.

...

>                                              Or might there
>be a short between the PC and Workstation side.  PC group has
>experienced no difficulty lately, so I doubt a short.

Definantly not shorted; the whole thing would go down immediately.

A filtering bridge would fix the symptom, not the problem. It sounds 
like you've got a PC with a card broadcasting garbage packets. Try 
turning off each PC and checking the repeater; when the receive light
starts acting like the one on the workstation side, you've found the
culprit. Fix it, and your PC users should see a considerable improvement
in response time and throughput.

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Many thanks to:

Peter Van Epp (vanepp@sfu.ca)
Pat Barron (Pat_Barron@transarc.com)
Jack Thomasson (Jack_Thomasson@SED.Provo.Novell.COM)
Kelly (kelly@jupiter.nmt.edu)
Mark Solsman (solsman@ra.nrl.navy.mil)
Rodney Campbell (rodney@cssc-syd.tansu.com.au)
Dave (dcc@!world.std.com)
Gary Heston (gary@sci34hub.sci.com)
Thad Phetteplace (tdphette@mke.ab.com)
Peter Graw (peter@iol.ca)
Stephane Bortzmeyer (bortz@cnam.cnam.fr)
Gil Kloepfer Jr. (gil@limbic.ssdl.com)

And any I've forgotten!

-Rick.
-- 
Rick Morris                            Email:  rick@sadtler.com
Sadtler Research Labs, Philadelphia   -But I speak for myself
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