I want to plug the old router (Westell) into the laptop and have the Westell talk to ARRIS. Is this doable?
Yes, but you shouldn't do it.
A bridged router (or in this case a modem/router combo) will no longer manage DHCP on your LAN, so any devices connected to it will look past/through it to the next DHCP host to obtain an IP address.
Normally, your laptop would get a local (LAN) IP address from the Westell, but if the Westell is bridged then your laptop will try to obtain a WAN IP address from your ISP. This is not only a security problem (since there is no longer a firewall between your laptop and the Internet) but may also cause problems with the new router obtaining a WAN IP address (many ISPs only allow you to have one.)
Therefore, if you want to bridge your Westell to your new router then you should also connect all of your end devices (including the laptop) to the new router. The only thing that should be connected to the bridged Westell should be the new router.
That being said, it is possible to bridge your Westell 7500. I would highly recommend that you disable the wireless functionality of the westell prior to bridging it (This will help prevent accidental connections from attempting to pull WAN IPs through the bridged Westell).
You could also disable DHCP in the Westell, but that step is probably unnecessary as long as you never connect more than one device to the Westell at a time using an ethernet cord (in most cases that device will be your new router).
Also, before bridging the Westell you will need to know some information about the connection from your ISP.
Is the connection using DHCP or PPPoE? You can find this information by logging into the Westell's user interface.
If the connection is PPPoE then you will need to know your ISP-assigned username and password (you will have to configure your new router to use PPPoE, which requires a user/pass to obtain an IP address).
To log into the Westell's user interface (UI) you will need to know its LAN ip address.
Most Westells I've seen use either:
192.168.1.1
or
10.0.0.1
Make sure you are connected to the westell with an ethernet cord.
If you put the correct ip address in the address bar of a browser then it should take you to the UI.
If neither of the above address take you to the correct page, then run ipconfig from a command prompt and find the Default Gateway.
Also, if you end up at some sort of search page, check to make sure your browser did not search for that address instead of navigating to it. You may need to include http:// before the address to prevent it from searching instead of navigating. (http://192.168.1.1).
Once you are in the UI, go to the Wireless section by clicking on the Wireless tab near the top. It should take you to a basic settings page where you can disable wireless by using a drop-down box (Wireless Operation - Disabled).
Click Save.
Now go to the Advanced tab at the top.
Click on the WAN sub-category; select VCs.
There should be a list for connections, but only the first one should be enabled.
Note the Protocol column, if it says PPPoE then make sure you know your user/pass before proceeding.
Click Edit at the end of the first row (the only enabled connection).
Use the drop-down box next to Protocol to select Bridge.
Click Save.
Disconnect the ethernet cord connecting the laptop to the Westell.
Connect the new router to the Westell.
Connect laptop to new router.
If your connection from your ISP uses DHCP then you will probably have internet access at this point.
If it uses PPPoE you will need to log into your router's UI and configure the PPP user/pass.
Good luck!
-Rom
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