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How to troubleshoot Network Slowness?


Always get complaint tat the network is slow but where or how i can start to troubleshoot from WAN or LAN Perspective?

Any free tools to assist?? or Any good start on how to troubleshoot this type of scenario??



Community Member

Re: How to troubleshoot Network Slowness?


We need more explanation about your network like where you are experiencing the slowness ??? With Wan or Lan ??? If you are experiencing issues with WAN what type of Internet connection you are using ??? If you have issues within you r LAN environment, then what kind of switches, VTP, Vlans and STP all needed to be known.

For troubleshooting, we need to understand where your having the slowness and the cause of the issues. So, give us a better explanation and from their we can go.



Re: How to troubleshoot Network Slowness?


A lot of ways to troubleshooting network performance issues, if its WAN problem you may go through the below troubleshooting steps:

1-Change the WAN interface load-interval to 30 seconds instead of 5 minutes (Default)by using this interface mode command "load-interval 30, then using show interface x/x is very useful

2-If your router not Cisco gear use any free bandwidth monitoring tools to monitor the current load on your WAN link.

3-Enable Net-Flow on your WAN interface and start check the top talkers on your network

2nd if the problem related to LAN switches, you may check the STP stability (IF enabled) Trunks load, errors...etc

More clarification about your issue will be nice.

Best Regards,

Mounir Mohamed


Re: How to troubleshoot Network Slowness?

First, try to localize the "slowness" if possible.

Are all of the complainers on the same segment? or the whole LAN, or just users that cross the WAN?

Is the network slow for users just going to the Internet, or just slow for users of the internal resources?

Some common "slow network" causes (depending on who is complaining):

One or more connections are having duplex-mismatch problems. This will usually cause extreme slowness. If the affected segment feeds a server, or an Internet gateway, everyone will see it.

Many times a "slow network" is really an internal resource that is slow to respond (maybe overloaded, maybe poorly written, old drivers, a user-class machine being used as a server)

DNS issues can make a network appear slow. Something like the primary DNS is down/offline/unavailable (or duplex-mismatched) so each request is timing out on the primary and failing over to the secondary ... the delay would appear something like the first web page takes "forever" to come up. Try another DNS server as primary.

Network (LAN) overload from virus/trojan/worm activity - do some virus scanning on the machines with complaining users.

Spyware - run Ad-Aware and SpyBot Search & Destroy on the machines of complaining users

WAN overload - if you use Frame-Relay, talk to your provider and ask for utilization stats for a day, or a week. They can usually provide a utilization plot for the requested time period (request it in advance, historical data may not be available)

Bad cabling - if you made your own cables, jumpers usually, and didn't use the EIA/TIA standards ... or if the cable are not terminated well, or damaged (crushed, severe bends, twisted, knotted, piled up behind the desk), it can cause a significant negative impact on the data transmission. Try replacing the cables with some "store bought" cables.

When a user complains of slowness, substitute your laptop for their PC and see if it's still slow. IF it is, then capture the traffic with Ethereal/WireShark (it's free) and look at what the traffic is actually doing. Lots of re-transmissions? Lots of CRC errors? lots of collisions / late collisions? "Sniffers' will also give you a timeline ... you can see what the actual response time is to/from a resource to help isolate the bottleneck.

Pings & Traceroute are sometimes helpful, but depending on your firewalls & fiters, may be blocked.

Check the utilization of your switches and routers. An overloaded switch or router will cause undo latency. Check your software/firmware versions and update as necessary.

Users using streaming applications, like BitTorrent, music downloads, video downloads .... find 'em and kill them (or at least get them fired). Make sure your Network Usage Policies are enforced. If you don't have Usage policy, make one, get the upper management to sign off on it, and start enforcing it.

There's lots more, but these can get you started.

Good Luck


Community Member

Re: How to troubleshoot Network Slowness?


Thanks for all your input. The slowness is through WAN Link from one remote site to another site at a DC. they claim tat the servers accessibility are slow and all of them are from same segment.

Anyway, I will follow the guidance above and get back to you guys if there is any finding..

thanks again!

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