Network is slow

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Jan 14th, 2008
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When users complain that the network is slow(the organizational network,aka "intranet") what show commands can i use in the switch and on what fields/parameters should i look that can point out that there is a congestion problem(the network is slow..)?

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Joseph W. Doherty Mon, 01/14/2008 - 12:48
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The two network issues that usually cause a "slow" network are either the high delay and/or high loss.

You might first ask your users to ping a couple of addresses and compare results between "good" network and "slow" network.

On your network equipement look for commands that show you dropped packets/frames or queue overflows.

mounir.mohamed Mon, 01/14/2008 - 13:41
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Plus the above tests.

I recommend to use any real-time software to monitor your internet link and external LAN traffic pattern:



Also "Show interface" command is usful in such cases in order to know if you have congestion or not., but keep in mind that this values changes every 55 minutes by default, but you can use the below command to reduce such interface to 30 seconds instead of 5 minutes.


Interface f0/0

load-interval 30

Chekc the input/output rate

Router#show int g0/0 | inc 30 sec

30 second input rate 367000 bits/sec, 68 packets/sec

30 second output rate 529000 bits/sec, 75 packets/sec

Pls rate helpful posts.

Best Regards,

Mounir Mohamed

glen.grant Mon, 01/14/2008 - 16:04
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you can get an instantaneous look at your interfaces and how much traffic is passing for all your interfaces using the "show interface summary" command . Easy to look at and see in bps how much is being tranferred . For fixed config switches the show controllers utilization is a useful command to see utilization % of all switchports and the switch fabric itself.

eriknixon Mon, 01/14/2008 - 19:35
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you could also enable NBAR to analyze the traffic for a few days to see what people are doing. If you have people on your network using P2p file sharing programs, or streaming a ton of video, you cold create QoS policies to give priority to important traffic while minizming bandwidth to less important traffic.


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