Sporadic slow down on LAN

I have been experiencing sporadic slow downs on my LAN. We have a Cicso 2500 router attached to a T-1. The backbone of my LAN is fiber and consisting of all 3Com switches. The packets flow really well 90% of the time and then it is like someone applies the brakes.

We do have a very busy State website, consisting of a standard HTTP and GIS sites.

Any ideas????

All will be greatly appreciated.

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cnorborg

My guess is your getting broadcast storms. Not sure how to check for them on 3com switches, I'd recommend pulling out a sniffer like ethereal and try to get more details.

I assume your keeping track of the bandwidth being utilized on your T1 also? Its very easy to overload one, esp. if its connected to the Internet.

You might want to upgrade that 2500 series router also, those are ancient. Cisco has some new routers that will handle a T1 great and have much better processor speeds and lots of nice new features. Something like the 1841 or 1760 would work well.

You could also get rid of all the 3com switches and move to all Cisco... 8-)

Craig Norborg
Network Analyst
Robert Bosch Corporation

pgpf

Broadcast storms are a possibility. I know you can graph the broadcast pps on the Routers interfaces with SNMP Grapher.

Try to use the 'Real-Time Interface Monitor', if you have it, on obne of those 3-com switches. Select "Broadcast/Multicast" on the statistics group and there you have those current values. Right-click on one of the statistics and graph that stat. Choose "Broadcast Packets Transmitted" and graph those. You'll then get a graph showing broadcasts. Next time the network slows down, look at this graph and you'll know if it's broadcast related.