[K12OSN] Excessive collisions cripple network -- Suggestions for solutions?

Tom Wolfe twolfe at sawback.com
Sun May 4 17:36:12 UTC 2008

Terrell & Julius, thanks for the ideas. The switches I have right now are 
Netgear GS748T (v1). They supposedly support STP but the firmware is also 
a little flakey. I'll give it a shot.

I'm also definitely into the idea of springing more $$ for better switches 
and moving the Netgears to other less critical locations. The Cisco 
Catalyst switches are expensive -- are they worth the money? Any specific 
recommendations? Any lower cost solutions that are "just as good"?

Tom Wolfe

 	Tom Wolfe, IT Specialist 	twolfe at sawback.com
 	Stoney Education Authority	tel: (403) 881-2650
 	Box 238, Morley AB, T0L 1N0	fax: (403) 881-2793
Morley Community School | Chief Jacob Bearspaw School | Ta-otha School

On Thu, 1 May 2008, "Terrell Prudé Jr." wrote:

> Julius Szelagiewicz wrote:
>> On Wed, 30 Apr 2008, Tom Wolfe wrote:
>>> Our Linux labs continue to work great. However, our network has now become
>>> much bigger, with lots of little satellite switches in our mini labs
>>> (classes that are serviced by a single Cat 5e wire now have 5-15 K12LTSP
>>> clients via simple switches).
>>> Every couple of months it seems that accidentally ?someone? plugs both
>>> ends of an ethernet cable into the same switch. This ends up sending out
>>> collisions like nuts and slows or cripples our network. I then have to
>>> figure out where the problem is and fix it.
>>> Are there any recommendations out there on how to prevent these problems
>>> from affecting my whole network, e.g. is there a switch that will shut
>>> down a port if it's generating too many collisions or problems? And maybe
>>> even email me to alert me of the problem??
>>> Suggestions would be appreciated!
>> Many optipons, all good options cost money. The simplest if not least
>> expensive is to use switches that support spanning tree protocol, end
>> enable it. There is a small packet delay penalty, but it is usually
>> negligible. All my HP Procurve switches have STP set and have no problem
>> with looped cabling. since this happens in rooms served by a single cat5
>> wire, local STP is really crucial. If only a big upstream switch has this
>> capability, it will stop all traffic from the affected room.
>> julius
> Julius is right.  What you're seeing probably isn't massive collisions,
> but rather a broadcast storm, which can happen even when everything's
> Full Duplex (i. e., no collisions).  Several models of switch support STP:
> HP ProCurve
> Cisco Catalyst (all models)
> Amer.com (all managed-switch models)
> Raptor
> Avaya
> I've also used some Nortel BayStack 350-24T and 450-24T switches, which
> do this job very nicely as well.  They make great LTSP switches, and
> they're relatively inexpensive on eBay.  Look for one with a Gig-E
> uplink in it.
> To get rid of the delay that Julius mentioned, which can take 30
> seconds, you should configure all your access ports for "Rapid Spanning
> Tree", or in Cisco parlance, "port-fast" spanning tree.  That'll reduce
> that delay from 30 seconds down to 2 seconds.  Leave your uplinks on
> "normal" spanning tree.
> Additionally, you might want to configure your access ports to do
> rate-limiting for broadcast frames.  This is relatively easy on any
> managed switch of decent quality.  We do this at my place of work with
> rather good results.
> --TP

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