OK, I think this is a gateway/modem or router/modem as many modern DSL modems are. This means that it has two separate networks. WAN and LAN.
WAN (Wide Area Network) uses the IP addresses that are seen by the internet world, like the 71.127.18.237 you mentioned. This is assigned to your modem by your ISP (Verizon) using DHCP protocol. Typically gateway modems should default with DHCP enabled and grab the proper IP address automatically.
LAN (Local Area Network) uses "internal use only" IP addresses. These can be assigned automatically (using LAN DHCP service enabled in the gateway and a DHCP service running on your computer) or assigned manually (using settings in your internet config area on your PC).
I suggest the following:
1) Connect your computer to your modem. Open a web browser (Firefox, etc..) and go to
http://192.168.1.1 (addresses that begin with 192.168 are LAN internal ones. I believe your router defaults to 192.168.1.1
2) Once connected to the modem, set WAN DHCP to enable, and LAN use the following:
Gateway 192.168.1.1
NetMask 255.255.255.0
3) Then go to your network config settings in your Linux and set the following for LAN:
IP Address: 192.168.1.2 (or 192.168.1.3 etc...)
Gateway 192.168.1.1
NetMask 255.255.255.0
Additionally, you can
download the manual for westell b90-210015-04 your here. It is in .doc format but you can open/read it with Open Office

With all that you should be set to go. Give a try and let me know if you have any other questions.