Path: utzoo!utgpu!news-server.csri.toronto.edu!mailrus!ncar!boulder!daemon
From: XJELDC@gemini.ldc.lu.se (Jan Engvald LDC)
Newsgroups: comp.dcom.sys.cisco
Subject: Re: strange behaviour involving repeaters
Message-ID: <23139@boulder.Colorado.EDU>
Date: 5 Jul 90 21:32:25 GMT
Sender: daemon@boulder.Colorado.EDU
Lines: 53

>Date: Tue, 19 Jun 90 17:13:43 -0700
>From: Greg Wohletz <greg%duke.cs.unlv.edu@RELAY.CS.NET>
>Subject: strange behaviour involving repeaters
>To: cisco@spot.Colorado.EDU
>Message-id: <9006200655.AA23113@spot.Colorado.EDU>
>
>We are experiancing some very strange problems.  First let me draw
>you a diagram of part of our network.
...
>        o       our cisco has 6 ethernet interfaces, the problem exists on
>                all of them.
> 
>So, for some reason the gateway is ignoring, or throwing away most packets that
>have passed through the repeater.  However, all our other machines can send
>and recieve packets that pass through the repeater without any
>problems.

I don't think the problem is the repeater, but the Cisco. We have the same
problems in a setup where we have two MT800s cascaded, to which about 10
Retix bridges, a Dataco remote bridge, a Dec VAX and two Ciscos are connected.
Everybody can talk to anybody, except host behind the remote bridge can not
talk through the Cisco. The Cisco decides that 80% of those packets are bad,
but an Ethernet monitor and all other equipment says they are OK.

This problem was introduced when we upgraded from old Ethernet cards to the
MCI cards. We swapped cards back and forth a couple of times and with old
cards we got 0 lost packets in 100000, with MCI we got 80% lost from the
Dataco bridge and 0.1% - 0.2% from any of the Retix bridges.

(Whenever we have had an error rate above 0.01% it has always been due to
some faulty hardware or configuration, so 0.2% is MUCH too high!)

The above problems with MCI cards was reported to Cisco via our Swedish
representative in autumn 1989, but Cisco didn't believe in it then. Later
this problem was recognised, as it has occured at other places too, and I 
have been told that there will be a firmware fix to the MCI card soon that 
will correct it.

I have no information on what the MCI card is doing wrong and how that
is corrected, though. For Ethernet trancseivers there are dedicated test
equipment that can tell you if the device under test is within allowed
limits, but I have not found any such test equipment that can test the
other end of the transceiver cable, the controller.
                                             
Jan Engvald, Lund University Computing Center
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