periodic network slowdown

[daniel espinal]

I need help. I've got 3 cisco catalyst switches and a cisco router all connected daisy chained.. The internet is really slow. I reboot the cable modem And the speed goes back to normal for a few hours then it eventually falls back to a crawl.

How do I go about getting to the bottem of this? I had an idea of mirroring the wan port somehow and plugging in a laptop with wireshark installed. The problem is I don't know what to look for.

[Phillip Wilson]

Do you have any Netflow or snmp monitoring on the connection going to you modem? To see if it is specific traffic or a computer eating up you internet pipe... How many devices do you have running through this cable modem? Sometimes cable modems have NAT/PAT limits. What speed of pipe do you have?

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[daniel espinal]

There are easily close to 100 devices.  Infact we ran out of ports so we've added a d-link and apple extreme both in bidge mode to accommodate some added devices.

I don't have any type of monitoring set up. I need to look into some freeware solutions. I was hoping there were some ios commands that would clue me into what is happening.

[Don Jacob]

Take a look at NetFlow top-talkers and see if any IP is hogging the bandwidth during the slowness. To use NetFlow top-talkers, you do not have to install any tool.

http://blog.alwaysthenetwork.com/tutorials/netflow-top-talkers/

If it is not a bandwidth issue (and I think it is not), you can use any monitoring tool to check the CPU and memory utilization, packet loss, etc. on the devices. Since you mentioned free, you could start with MRTG or Cacti to get a basic picture and then go on to try Nagios XI or Spiceworks, etc. for complete network monitoring.

Regards,
Don Thomas Jacob

Head Geek @ SolarWinds Inc

NOTE: Please rate and close questions if you found any of the answers helpful.

[daniel espinal]

Thanks everyone for your replies. netflow is something I definitely have to invest in. As far as the problem goes it seemed to be a DNS issue I was using Google DNS and it worked for a while all of a sudden it has been causing problems on the WAN. I switched back to Time Warner DNS and have not heard a Complaint since.