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



I guess it depends on what you're looking for.  If you're looking for just *one* switch, specifically for a K12LTSP lab, then you can go with pretty much any of the managed switches below.

On the other hand, it sounds from your initial email like your site has a "cobbled-together" network infrastructure consisting of CompUSA-grade mini-switch devices.  If I were you, I'd be looking at a wholesale upgrade of the wiring closets.  That's what we did in my district.  We got rid of all the Synoptic LattisHubs and other substandard gear like that and put in some decent gear.  We have emphatically not regretted it.

Catalyst switches are definitely good stuff, though they are definitely expensive...if you buy them new.  If I were you, I'd get on eBay and have a look for the Catalyst 3550, the 48-port version, and make sure you get the two GBICs along with it.  They very often can be had for less than US $1,000.

I used to recommend Amer.com's SR48G2i (US $995).  Unfortunately, not only do they not make that model anymore, but I've also found that the company is somewhat less than trustworthy.  They made promises to us that, once they thought they had our money, they demonstrated no willingness to keep.

--TP
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Tom Wolfe wrote:
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"?

Regards,
Tom Wolfe

---
    Tom Wolfe, IT Specialist     twolfe sawback com
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On Thu, 1 May 2008, "Terrell Prud� 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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