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New Member

Troubleshooting router to switch connection.

I have a router connected to a switch via the ethernet ports. Problem is the connection will begin to lose packets out of the blue. At first some of the equipment connected to the switch was losing network connectivity. So we power cycled the switch and everything seemed fine. Then about 5 days later the same thing started happening again. I tried pinging the switch from the router with 1000 repeats and about half of them didn't come back. So thinking since rebooting the switch seemed to fix the issue last time maybe the porblem is with the port on the switch. I decided to to try moving the connection to a different switch port. This time 100% of the pings returned. So I moved the cable back to the original port thinking that maybe it was just bad. Tested again and again 100% of the pings returned. So then I figured maybe it was just a bad connection and now that the cable had been reseated it would be ok. Several days more go by and the problem starts happening again. This time no one was on site to assist so I figured I would try to figure out what I could while the problem was going on. I rebooted the switch and this time it didn't help. The connection was still losing half of the pings. Then I rebooted the router and it was "fixed" again. I know its just going to start happening again in a few days because its been going on for a couple weeks now. I'm going to try and replace the cable and see if that helps but I'm not convinced it will.

Is there any tests I can run to try and determing if the problem is on the switch's ethernet port or the router's ethernet port? I'm trying to see if either on of them show some kind of errors so if neccesary I can have them replace the proper equipment.

I've only been at this a little over a month so anything you can tell me to help me learn would be great.

VIP Super Bronze

Troubleshooting router to switch connection.

What type of router and switch do you have?

When you issue sh int x/x do you see any error massages (output error, input error, runts, giants, etc..)?

Can you post "sh run" from the switch and the router?


Hall of Fame Super Gold

Troubleshooting router to switch connection.

Aside from what Reza has posted, what is your exact switch model?

New Member

Troubleshooting router to switch connection.

It is a 2811 router and a 2950 switch. I don't see any errors on the router's fa0/1 in 22 hours or on the connecting fa0/22 interace on the switch. As of right now everything is working again since I reloaded the router yesterday.

I think I ready something that said if you ping across the switch to a device connected to it the switch will pass those traffic with normal priority instead of a lower priority if you sent pings to the switch directly. Is that true? Next time the connection starts having problem I would like to get some traffic going across it to see if any errors happen on either of those interfaces. My thought is that if I can see errors and determine if they are input or output erros that would give me any idea on which interface is having the problem.

I would prefer not to put up running configs, I'm not sure how my company would handle that and I would honestly just prefer to figure it out on my own thant to show you the configs and just have you point out the problem. So for now lets just assume the configs are correct as they have not been changed in well over a year and the problem just started a few weeks ago.

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