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New Member

Flapping LAN Connection

Hi, Recently i noticed our internet connection suddenly became very slow. While troubleshooting i noticed connecting one system directly to my IDU i get satble replies from my external DNS, but when i connect to the LAN i get something like

Reply from 199.?.?.?: bytes=32 time=827ms TTL=233

Reply from 199.?.?.?: bytes=32 time=906ms TTL=233

Reply from 199.?.?.?: bytes=32 time=1048ms TTL=233

Reply from 199.?.?.?: bytes=32 time=1143ms TTL=233

Reply from 199.?.?.?: bytes=32 time=995ms TTL=233

Request timed out.

Reply from 199.?.?.?: bytes=32 time=1208ms TTL=233

Request timed out.

Request timed out.

Reply from 199.?.?.?: bytes=32 time=1363ms TTL=233

Request timed out.

Reply from 199.?.?.?: bytes=32 time=1483ms TTL=233

Request timed out.

Reply from 199.?.?.?: bytes=32 time=1392ms TTL=233

Request timed out.

Reply from 199.?.?.?: bytes=32 time=1207ms TTL=233

Request timed out.

Reply from 199.?.?.?: bytes=32 time=1117ms TTL=233

What could be the explanation for this. I have tried to isolate switches and systems, i realised it is either one of the switches or a device connected to it. My question is, why does this happen why does it affest the entire LAN. What can i do?

Thanks

Toyin

3 REPLIES
New Member

Re: Flapping LAN Connection

I would investigate hop by hop. Do a traceroute to your destination and see where the slow down starts. That will give you a better handle on where to troubleshoot. Once you locate the problem area run a sniffer to troubleshoot further. It could be as simple as a bad NIC card chattering away.

New Member

Re: Flapping LAN Connection

Hi, Adam, thanks for your response. The traceroute seems to be showing me something, but i don't know what a sniffer is and how to use it. Could it be used on a switch as well? Where can i purchase on download it.

Thanks

Toyin

New Member

Re: Flapping LAN Connection

Hi Toyin;

I'm not advertising a product but my favorite sniffer is Ethereal and it's free!!! Just surf to www.ethereal.com and download. If your using cisco switches then setup SPAN - do a search on TAC as it can get detailed. Is it possible for you to upload the config of the switch where your having trouble. Also output of show interfaces of your ingress & egress interfaces would be helpful. I've seen instances where speed/duplex mismatches have caused such problems.

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