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Re: Collisions

To: nv-l@lists.tivoli.com
Subject: Re: Collisions
From: Jeff Fitzwater <jfitz@PRINCETON.EDU>
Date: Thu, 14 Oct 1999 09:35:58 -0400
Hope this helps.

My two cents on collisions.

        Monitoring collisions is not as easy as one would think.  First
you
must understand what you want to see.  You can only see packet
collisions on a local segment, before any repeater.  Once the collision
hits a repeater it strips it and sends out a JAM pattern to all other
ports, except the one it came in on, assuming you don't have a tap that
has SQE turned on. (That's a no-no).  The JAM pattern is sometimes
referred to as a remote collision and can be detected by a good
analyzer.  Don't mix up the term LATE collision with LOCAL or REMOTE.
These are packet collision that occure after 52uS of transmission and
indicate a transceiver is bad or you have exceeded the max distance for
packet propogation (cable too long or too many repeaters).
         To see LOCAL collision your mib agent must support RMON (in 99%
of
cases), which has this variable along with other common local
etherstats.  I
have never seen an agent that shows REMOTE collisions (JAMS).  You may
see them as frags with a pattern of all ones, which could equate to
ASCII (5 or U).  Keep this in mind when you are looking for collisions
but don't see any.

I believe the correct MIB to use is RFC1271 RMON.
It is normally already loaded in NV mib browser and is under mib2.

I use it all the time for the basic RMON etherstats.
All other RMON tables require setting control tables first and is much
cleaner with an RMON tool.  I use Cabletron SPMA RMON tool which works
for almost all devices that support RMON.

Jeff Fitzwater
CIT Systems & Networking
Princeton University

"Joel A. Gerber" wrote:
>
> Christian,
>
> Sorry for the delay in replying, but it appears that no one provided you
> with the RMON MIB for collisions.  If you have a device/probe with RMON
> capabilities, then it is another possible source of monitoring collisions.
> It is in the RMON etherStats table, which is at
>
>         .1.3.6.1.2.1.16.1.1.1.13
>
>         -----Original Message-----
>         From:   Joe Fernandez [SMTP:jfernand@KARDINIA.COM]
>         Sent:   Friday, October 01, 1999 21:59
>         To:     NV-L@UCSBVM.UCSB.EDU
>         Subject:        Re: Collisions
>
>         Collision counter MIB variables are in the Ethernet MIB and in
> various
>         vendor enterprise MIBs.
>
>         The snmp_mibs directory on your NV system should contain the
> Ethernet MIB
>         either in its January 1993 version as RFC1398, or a later version. (
>         RFC1398 has subsequently been updated and made obsolete by RFC1623,
> then
>         RFC1643, then, for SMI v2, RFC1650, RFC2358, and finally RFC2665. I
> suggest
>         you load the latest one of these that you can find on your system.)
>
>         However, even RFC1398 has a dot3StatsTable which has (among other
> counters):
>         dot3StatsSingleCollisionFrames
>         dot3StatsMultipleCollisionFrames
>         dot3StatsLateCollisions
>         dot3StatsExcessiveCollisions
>
>         Various vendor enterprise MIBs also have collision counters, so I
> would
>         also look in the appropriate enterprise MIBs for your
> hub/switch/routers,
>         try Gets on both sets of variables and compare them.
>
>         Finally, I would, if possible, put a protocol analyser on for a
> short
>         period to verify that correct counts are being reported in the SNMP
> MIB
>         variables.
>
>         At 10:14 AM 10/1/99 +0200, you wrote:
>         >Is there any way of messuring collisions with snmp?
>         >
>         >I haven't found a MIB-variable for it anywhere, does it exist?
>         >
>         >
>         >-----------------------------------------
>         >Christian Frantsen
>         >Technical Operations
>         >
>         >Internoc Scandinavia AB
>         >Tel: +46-36-194843
>         >Fax: +46-36-194651
>         >http://www.internoc.se
>         >
>         Joe Fernandez
>         Kardinia Software
>         jfernand@kardinia.com
>
>         http://www.kardinia.com


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