DSL to cable and back - Cannot acquire IP address

[coil_nine]

We started on Comcast cable. We also installed DSL Verizon to compare them. Currently we have both services into the house. Problem is, once a computer has been set to connect to the DSL modem, it cannot acquire a network address from the cable modem.

Previously, I successfully set up internet access through the cable modem, both hardwired and wireless

Then I disconnected from the cable modem and successfully set up the internet access through the DSL modem. It required me to install Verizon software

Here is the problem:
Now I disconnect the cat 5 from the DSL modem and connect it to the cable modem. I cannot acquire a network address.

I think the Verison software has made some changes that prevent acquiring a dynamic network address from the Comcast cable modem.

What settings might I need to change to acquire the cable modem address, and where would I look for it?

Verizon - Westell 6100 DSL modem
Comcast - Motorola SB5120 cable modem

two computers, both running Windows XP os

[YeOldeStonecat]

Cable modem only requires the LAN adapter to be set to "Obtain Auto".
The Westell should be the same....as it's really a router that already does the PPPoE for you.

[coil_nine]

it is set to "obtain auto". It acquires the DSL modem address. It does not acquire the cable modem address.

[YeOldeStonecat]

Is there a PPPoE adapter setup on the computer? Usually with the Westells..the modem/router itself does the PPPoE for you..you don't have to install/configure your workstation for it. Normally the Westells run as a router..so the PC gets a 192.168.0.xxx or 192.168.1.xxx address.

With Comcast...you should get a public IP address from the Surfboard.

Are you getting a 192.168.100.xxx address from the Surfboard? If so..your surfboard isn't connected to Comcast properly...it's not getting a public IP address from them.

[Tech Manager]

It is possible that you are holding on to a previous DSL settings. Are you doing a release and renew through ipconfig?