Slow Lan Performance

Unanswered Question
Feb 28th, 2007


I am facing poor lan performance in my network. My applications are not working properly.

All this started to happen when I did a LAN upgrade. I replaced all of my Cat5 cables to CAT6 cables. Do by any chance this can be a reason ?

Can anyone give a hint regarding this ?



I have this problem too.
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This is a huge question. The simple replacement of cabling would not normally cause this.

And the definition of poor lan performance is as wide-open a question as "my car is making funny noises, what should I do"

I recommend that you collect performance complaints and see them occur yourself, be able to reproduce the complaint, if it's a single app/network, you've narrowed it down, if not, is it app specific, a single server or server farm, building, room? Lots of stuff to divide and isolate what the real problem is.

1st - Turn on Logging, log everything you can, short of debug all outputs (might slam the gear CPU to the point of failure, non-repsonse)

Classically I'd recommend the Cisco-blessed bottom-up approach.

Layer 1. Check all port/interfaces for physical layer errors, misconfigurations, speed/duplex mismatches, etc. Fix, recheck, etc. Are you seeing hi-cpu loads on any gear in your network.

Layer 2. Look at ARP tables,default routes. Up/down situations on interfaces. Spanning-tree, check status, logs, debugs, any loops, execessive BPDUs? Flapping interfaces etc.

Layer 3. Systematicaly ping from an end-station experiencing the problem through your network, any huge latency issues? See where it slows and check that device. Are you getting a ton of broadcasts - sniff segments and see. Apply remedy as you find issues. Run traceroutes, look at routing tables in each router... anythink look funny? Fix and move on.

Layer 4 - 7 -- Sniff, baseline tftp/ftp tests from a work station to an access-lever switch and then out 2 or 3 devices in your network. Any major changes in delta times? Look for heavy ACL activity at each device.

This is just a very very basic summary of what you need to do. Use CCO and do searches on each level of troubleshooting.


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