I’m having some problems connecting an adsl modem to a 4 port router (both dlink boxes).

I take the dlink router ( D-Link DI-704UP ) back to office to test with my ADSL system.

Before I get a chance to properly test the router, my ADSL modem/router ( netcomm nb1300 plus 4 ) fails after 13 months (it had a 12 month warranty… grrr). So I quickly buy a single eth port router ( billion bipac 5102s ) & I connect it to my existing router (tp-link tl-wr642g, 4 eth ports, 1 wan port & a wireless AP).

I then notice that my original setup (the connection to the wireless router) doesn’t look right. It works, but the wireless router has 4 eth ports & a wan port & I didn’t connect the wan port to the original modem. The modem was connected to the second router via one of the standard ethernet ports on both boxes.

I decide to look into this further, as I might encounter many similar situations.

With next to no information available on the internet (or in the manuals) on how to connect an adsl modem & a router… I experiment a bit & I find 2 different ways to connect them:

How it should work: modem is set to bridge mode & then connected to the wan port of the router… The modem should now ignore its ISP details (I’m assuming a PPPoe internet connection, which requires a username & password). It should also ignore its DHCP & firewall settings. Now I enter isp details (username & password) into the router & make sure the router firewall settings, DHCP, etc, are appropriate. I can now connect 4 computers to the 4 router ports. The router is logging in to the ISP, with the modem acting as a conduit for the network traffic

Messy workaround: modem is set to router mode (make sure the DHCP server, firewall, etc., are enabled). The modem needs the PPPoe username and password. Connect it to one of the 4 ethernet port on the router (NOT to the wan port)… Make sure the routers (fixed) IP address is set to be in the same subnet as the modems IP address & DHCP pool eg: modem is 192.168.0.1, dhcp pool is 192.168.0.3 – 192.168.0.34, so change router IP address to something like 192.168.0.111. Now, disable DHCP on the router… let the modem do the dhcp allocations.
Reboot all devices & computers. Note that this time, the modem is acting as the nat firewall (instead of the router).

advantage: works with modems that don’t have a bridge mode (ie will work with all adsl modems)
disadvantage: you lose 1 ethernet port… so only 3 computers can connect instead of the usual 4.

Anyway, I take the router back to the customer & find that his modem doesn’t have a bridging function (but it allows for NAT to be switched on & off… not sure why)… So I setup the system the “messy” way, and setup shared windows drives.

There is a slight hiccup with being able to view the “program files” folder, but I put it down to an interaction problem between winxp pro and winxp home.

I leave it for the moment, as I also want to setup the print server function that is available with the router (it has a usb port).

I install the printer server software from the router CD, and then what? The manual is no help, & I don’t know how to print to the print server. I eventually decide to just connect the printer locally & share it out, so that the other computer can also print to it. Not as nice as using the print server function, but it works & its quicker than trawling the ‘net for an answer.

Update (June 2008 ): I’ve since found that most modern routers will now operate correctly by plugging the modem into the WAN port of the router. Very little else needs to be done… but some manufacturers still have WAN ports that don’t function correctly (particularly when isolating DHCP and IP addresses.