Assistance Configuring ISR2811 Behind Dynamic IP Comcast Cable Modem

Answered Question
Apr 28th, 2008

I am attaching two files:

1. ISR2811-to-CM is the configuration for the router that is behind Comcast Cable Modem.

2. DHCP-Debug is the debug monitor report for DHCP behavior.

I am almost left to believe that Camcast may be filtering dynamic DHCP.

Thanks for the help.


Correct Answer by a.cruea1980 about 8 years 10 months ago


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Thanks. Glad I could help.

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Overall Rating: 4 (1 ratings)
a.cruea1980 Tue, 04/29/2008 - 07:02

For one, I can tell you that you don't need your ip route. DHCP will give you your route.

Have you reset your modem since hooking your router up to it? If there was a device on your modem before hand, the modem may need power-cycled.

Other than that, your config for fa0/1 looks fine, but set duplex to auto as you have "speed" set, too.

wil.cassell Tue, 04/29/2008 - 07:35

Yes, a wireless router was previously connected to the cable modem. The effort is to replace it with the 2811. No, I did not power cycle the cable modem after connecting the 2811 to it. I will try that and configure the speed on Fa0/1 to auto consistent with the duplex. Good suggestions. Thanks.

wil.cassell Tue, 04/29/2008 - 20:01

Thanks again. It works just fine now. I power cycled the Cable Modem and adjusted the interface speed to auto consistent with the duplex.

Onto tinkering with IPS now.

Thanks again.

Correct Answer
a.cruea1980 Wed, 04/30/2008 - 05:27


If you could, mark this as "solved" for others.

Thanks. Glad I could help.


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