Cannot ping 1811 router when unplug a switch

Unanswered Question

We have a Cisco 1811W router for our connection to the Internet and multiple Catalyst 2948 and Dell 5324, 5448 switches in our network. We have a single subnet network. I recently unplugged one of the Catalyst 2948 switches from the network and about 5 minutes later our router stopped responding. (I could not ping it's inside interface I plugged the switch back in, and after a minute I could ping the router again. The switch and router are both plugged into the same Dell switch.

The Router internal IP address is We have NAT, the Firewall and Wireless Interface configured. The Catalyst 2948 configuration IP is We do not use separate VLANs. I don't know a lot about router and switch configuration, but I looked through the configurations on both and didn't see anything obvious. I would appreciate any help to solve this problem.


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Chad Peterson Wed, 08/18/2010 - 10:06

Hi Jason.  This seems a little strange.  I'd be interesting to see what the arp table on everything look like when you unplug that switch (I'm assuming the path from your PC to the router doesn't go through it )

Ping the router from the PC in the working scenerio, then collect 'arp -a'

From the router collect 'show ip arp '

Now unplug the switch

Clear arp on PC 'arp -d '

Clear arp on router 'clear ip arp ' (or mabey its a clear arp command)

Ping the router from the PC, collect 'arp -a'

Again from the router collect 'show ip arp

Just wanting to start here at the basics...see if something is changing here that could explain the behavior.


The router seems to be working right now even with the switch unplugged. I was following your steps and unplugged the router. I was waiting for it to stop responding and it didn't. I will watch it a while before considering it fixed. If it fails, I will capture the arp info. Thank you for taking the time to help.

Chad Peterson Mon, 08/23/2010 - 10:23

Great to hear.  If the issue does come up, or anything that feels like this...collect the commands listed above.  It can help us understand a little bit about what is wrong here.


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