getting a 2811 to connect to a cable modem

Unanswered Question
May 13th, 2010

I have a Cisco 2811 connected to a cable modem , and i cant get it to get an IP. i am able to get an IP with a workstation and a Pix 501, but not this device. Based on the below, does anyone know a reason why i wouldnt be able to get an IP? i recently added this to tinker arround (replaced a linux distro router), and i cant figure out why it wouldnt be able to get an IP...

interface FastEthernet0/1
description $FW_OUTSIDE$
ip address dhcp
ip access-group 101 in
ip nat outside
ip inspect SDM_LOW out
ip virtual-reassembly
ip route-cache flow
duplex auto
speed auto

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TechnicallyCreative Thu, 05/13/2010 - 13:14

note:

yes, i have restarted the router and the modem multiple times.

yes, i did leave the modem unplugged for 15 minuets.

Giuseppe Larosa Thu, 05/13/2010 - 23:15

Hello Danielle,

two features could be blocking DHCP message exchange:

the applied access-list

ip access-group 101 in

and CBAC

ip inspect SDM_LOW out

as a first troubleshooting you could remove these two commands using

int fas0/1

no ip access-group 101 in

no ip inspect SDM_LOW out

if after this change your router gets an IP address you will need to tune these two feature configuration

Hope to help

Giuseppe

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