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New Member

Help troubleshooting 2600 router connection issues

I posted a message a few weeks ago about this problem, so here is an update with further questions.

I had a Cisco 2620 router that was dropping all LAN and WAN connections at random intervals. When the router would "go down", I could not ping the local LAN IP address of the router, nor any IP address on the WAN side of the router. The router also routed LAN/WAN internet traffic, but internet access was not affected when the router lost connection. The router would be down anywhere from 8 - 15 minutes, then restore the connections. Sometimes the router would go down for longer, then I'd have to reboot the router, and the connections were restored. Last week I replaced that router with a brand new Cisco 2620XM (on loan), configured it exactly like the older router, and it is doing the same thing. The old router had been working fine for about 1 year before this problem started happening.

Some of the suggestions I got were to manually change the speed and duplex settings on the router and the LAN switch it is attached to. The switch is an HP ProCurve 4000. I manually set the router for 100m speed and half-duplex, and set the port it was attached to on the switch for the same settings. It made no difference. I also tried other settings (full duplex, auto, etc and got the same result). I contacted HP, and after running diagnostics, they say there's nothing wrong with the switch.

Is the router simply not able to keep up with the routing requests and taking itself offline? I've only got 35 users on the LAN and 65 users on the WAN, this router shouldn't have any problem with the load. The only other thing I can think of is a computer with a virus that's bombarding the router with data, but the router still does this when I disconnect the WAN (and I know all the computers on the LAN are clean). Any other ideas?


Re: Help troubleshooting 2600 router connection issues

When you lose connectivity what does it say in the logs? CPU usuage etcc.... Is the cpu ok when this happens , do the logs indicate that any interfaces actually went down or will it just not route when this happens . That isn't very many users and unless some user is doing someone that is burying the router for some reason then you should be ok . When you say you could not ping the interfaces were you right on the router or were you trying to ping from a remote location ? Are there any interface errors on the ones that you are having a problem on ? Take a step by step approach and look at the logs , cpu, interfaces etcc.. when the event is happening .

If all else fails you may have to get a sniffer on the lan and see if there is anything going on seeing that it happens with WAN even disconnected . You could try turning on ip cache flow on the interfaces if your router supports that and see what the flows look like and see if one person is doing a lot of the traffic . We used this effectively when fighting blaster and slammer worms , good tool . don't know if yours supports this or not ..

New Member

Re: Help troubleshooting 2600 router connection issues

I'm not really too familiar with Cisco's logging system, so I probably missed something. Here's what I've checked so far:

- The Console Logging and Trap Logging have entries, but I have no idea how to look at them.

- When I do a #show buffers, the Small, Middle, Big, etc buffers look ok. The Header Buffers shows a total of 137, with 9 in free list (128 in use somewhere). The FastEthernet0/0 shows a total of 192, with 0 in free list (192 in use somewhere). The Serial0/0 shows a total of 48, with 0 in free list.... I don't know if that's normal for the Ethernet and Serial ports.

- I do have ip cache flow running, and it looks like normal traffic patterns. Is there anything in particular I should look for?

- I also ran #show interfaces switching and #ip interface and didn't notice anything out of the ordinary. Again, is there anything in particular I should be looking for?

I noticed a few other things too. When the router is down, and I connect through the console port, I can ping addresses across the WAN. So the issue appears to be centered around the router's LAN connection. Most of my ping tests are from my workstation on the LAN, so when I say I can't reach ip addresses across the WAN when the router is down, it's from a ping test from my workstation. I also noticed that the router recovers as soon as I run a command through the console. For example, the router goes down and I connect a laptop to the console. I log in, run a show command, and within 10 seconds the router is back up. Strange.

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