dhcp problem on wan interface of 871 router

Unanswered Question
Mar 26th, 2007

I recently purchased a cisco 871 for use at home with a cox business line.

For initial setup/testing I had connected it to a linksys router but it would not receive an ip address. After beating my head against the wall for an hour, I read somewhere that dhcp will not work with a non-routable ip address on the wan link.

So I went ahead and plugged into my cable modem, and was able to pull an ip address from cox.

The problem is that after a random period of time it would stop routing traffic out the wan interface. All routes still showed up as they should, and I did not touch the config. A release/renew dhcp would fix the problem for another random amount of time (would pull same address).

I then brought it into work with me, and it will not pull a routable ip address from our campus dhcp server. debug dhcp revealed the following error which I was initially getting when hooked into the linksys:

"unknown dhcp problem.. no allocation possible"

if I assign a static ip address on wan interface, everything works fine.

i have also tried this with a completely clean config file (other than ip address dhcp entry on wan interface) with the same results.

linksys router worked with no problems.

any advice would be greatly appreciated.

I have this problem too.
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Amit Singh Mon, 03/26/2007 - 08:58

Please paste the config of the router.

Are you using a fast ethernet port as a WAN port. if yes, then have you tried using the command " ip address dhcp " under the interface to recieve an ip from the dhcp server.

HTH,

-amit singh

cgoesch@gmail.com Mon, 03/26/2007 - 09:10

yes, and yes.

from a pc connected to my 871, i initiated a ping -t to the gateway router (cable modem). everything works fine initially. but then after a random period of time (anywhere from 5-10 minutes that I observed) the pings begin to fail.

if i then go to my 871 router and issue release dhcp and renew dhcp commands, the pings are then again successful for another random period of time.

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Posted March 26, 2007 at 8:43 AM
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