09 Feb 12 Cisco Soho 91 Basic Configuration

How to configure Cisco Soho 91 Router for Basic Connectivity

I needed to configure a Cisco Soho 91 router for my home to work with Comcast Cable – Dynamic IP. I was looking for a basic config online that I can just copy and paste and wasn’t really able to find any so I started to configure it from the scratch. It was just simple basic configuration however I was having an issue getting the IP Address on the WAN Interface – Ethernet 1 from the Comcast Modem. I reset the modem, called Comcast and tried to work with them no use, rebooted the Cisco Soho 91 multiple times, left it plugged into the modem for a long time, left them both off for a while and turned them back on but no use. So lets see what I did and what caused the issue. First I’m going to go over the basic configuration:

Internal DHCP Server Configuration on Cisco Soho 91

ip dhcp excluded-address
ip dhcp excluded-address
ip dhcp pool dhcp_pool
import all
lease 5
ip dhcp-server

So I started doing debugging and saw these DHCP debug messages:

*Mar 1 00:16:09.655: DHCP Offer Message Offered Address:
*Mar 1 00:16:09.655: DHCP: Lease Seconds: 3600
*Mar 1 00:16:09.655: DHCP: Server ID Option:
*Mar 1 00:16:09.659: DHCP: offer received from
*Mar 1 00:16:09.659: DHCP: offer: server not in approved list
*Mar 1 00:16:09.759: DHCP: Received a BOOTREP pkt Not for us..: xid: 0xAAA0E5B3

Now if you look at the debug it is clearly telling you that the DHCP server that offered the IP address to the WAN Interface is not the approved server. Well after looking at the Soho 91’s configuration I found the following line to be the culprit: “ip dhcp-server”. Basically I disallowed any other servers to act as a DHCP Server and offer IP’s to the routers WAN Interface. Hope this will help some one out in future and one line won’t waste an hour of your time :).

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