Tag Archives: 4 port router

connecting a cable modem to a 4 port router / wap

Computer Aid Posted on by

This is a slight rehash of one of my previous articles ( http://computer-aid.com.au/blog/2006/04/28/connecting-a-dsl-modem-to-a-4-port-router/ ).

A customer had an optus cable internet modem (connected to his pc via usb). He had purchased a wireless router (d-link) and asked me to set it up (as well as a wireless pcmcia card for his laptop & a second computer).

At first glance, I think: hey, easy… its not a telstra cable internet, and I once had optus cable internet & a router connected at home, so maybe 1 hours work).

Well, I'm now so used to adsl, that I forget to do some reasonable checks:

  1. When I change anything, refresh the network settings (or even restart all the network devices)… Not doing this can cause confusion & excursions down 'one-way streets' (ie: what the h*ll is going on here?).
  2. If something doesn't make sense, keep investigating, until you understand it.

When the PC is connected directly to the modem, the ipconfig /all command shows the optus gateway & dns servers. I setup the modem & router to use the same IP subnet (192.168.100.xxx). Figuring out the modem IP address was tricky… as it doesn't show up in ipconfig! I had to go to the motorola website to find out!

I disconnect the usb between the modem & the PC, then connect the modem to the router WAN port via ethernet, then PC to router (ethernet)… but it doesn't work well (here is where I should have restarted the modem/router/PC)…

I figure the modem isn't made to work on the wan port, So I'll use the "messy workaround" (ie avoid using the WAN port). It works, but ipconfig still shows the optus gateway & dns servers. This is where alarm bells should have rung, and I should have followed point 2 above.

I now setup the laptop wireless card. It connects to the router, but no internet connection. I also try the second PC, & it also cannot connect to the internet.

I'm really puzzled… 3 PCs connected to the router, but only 1 can see the internet… why???

Eventually, I try 3 wan port configurations (dhcp enabled on only the modem, and dhcp only enabled on the router, and dhcp enabled on both). After doing a correct restart every time, I find that the ipconfig settings look normal (ie gateway & dns settings correspond to the the router address) when only the router is setup for dhcp.

I then restart the laptop: hey, it works! The other PC also works now.

Although the cable modem is slightly different from an adsl modem, the overall setup is still very similar.

connecting a dsl modem to a 4 port router

Computer Aid Posted on by

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.