How to convert a wireless ADSL router/modem to just an access point and a modem and use an external Linux box as a router (internet gateway)

Question

My home network setup is just a typical one. A "dump" box from Vodafone containing everything (ADSL modem/router + 4-port Ethernet switch + Wireless access point).

Since I am kind of a techie, I don't like that kind of setup and I need to be able to configure everything by hand (NAT using iptable rules, etc.). So, I decided to setup an external Linux box as the router (Internet gateway) for the rest of the LAN according to this guide: http://www.gentoo.org/doc/en/home-router-howto.xml

So, my question is: Is it possible to just leverage the Access point and the ADSL modem functionality in the dump box while using the external Linux router so that I don't need to buy both (modem + AP) separately?

Googling on the issue of the AP I know it can be done by disabling DHCP in the dump box and using a DHCP server in the Linux gateway with an IP address range that doesn't include the IP address of the dump box. The issue with me is that I want to do BOTH things (The AP and modem).

The thing that confuses me the most is how to bypass the PPPoE configuration in the dump box so that the one in the Linux box can take effect without conflict, specially that the configuration interface for the dump box doesn't contain any controls for disabling PPPoE. It just contains fields for the parameters (like username, and password, etc.). Or am I a bit pessimistic and things would just work once I configure the hosts on the LAN to use the new Linux gateway?

Any help would be really appreciated. And thanks for your time.

Answer 1

You should be able to just chain them. I have an Apple Time Capsule behind my provider's ADSL gateway (modem/router/AP). The Time Capsule warned me about double-NATting during setup but allowed it, so I effectively have two NAT firewalls. It's been in use for several years with no ill effects I can see.

Answer 2

The way that ADSL is usually handled is to put the modem into bridged mode, and run a PPPoE client on the Linux box. The modem then simply provides transport between the Linux box and the access concentrator, and the Linux box has the credentials for creating the connection and is responsible for routing traffic through the ADSL connection.

In terms of DHCP you want to setup a DHCP server on the Linux box, and disable the DHCP servers on both the modem and the API. You probably want to give the modem and AP static IPs on your subnet so that you can access them for management.

Answer 3

1. If I am right you used to have a DSL wire (telephone cable of the standard RJ11) that was plugged/ inserted into a wired/ wireless modem. The wired/ wireless modem was/ wasn't configured to dial/ connect to the Internet. And that is how this system works. One peculiar security feature DSL provides is port binding. The username and password being grouped/ locked to the telephone number is an act of port binding. This way, nobody except you (having known the telephone number as well as the login credentials and also to have physical access to the wire) can use the connection to access the Internet.

2. To this counterpart, all that changes with the wireless modem to being a wireless access point/ wireless router is that instead of a RJ11 (WAN) DSL telephone cable, there exists a RJ45 (WAN) Ethernet coaxial cable. Again, it may or may not be configured to connect to the Internet. The security peculiarity of this set-up is that the username and password is provided successful authentication via the registered MAC address of the networking hardware exclusively on the ISP's server. This way, nobody except you can use the connection to access the Internet.

3. What you want to achieve is only partially possible with the current set-up. Progressively, note down your wireless modem's IP address and disable the DHCP (automatic IP addressing to the connecting devices) so that the router only acts as a bridge. Now, manually (statically) configure the LAN/ WLAN card on your device to connect to that wireless modem as the DHCP would have. Conclusively, dial/ connect to your ISP's servers and there, you're connected to the Internet via a WAN (RJ45) cable from a wireless modem.