Why can't my router see the internet, when my computer can?

August 18, 2009 9:55 AM

Networking question: I have a wireless router (well, 2, actually, as I thought the old one was faulty so just bought a new one) but it can't see the outside world. If I plug my computer directly into the modem, I can use the internet. If I plug a router into the modem, it can't see the internet. (I can connect to the router via wireless or wired, but the router can't connect any further.) Any ideas what this might be?

The modem is a standard "NTL" (now Virgin Media) box. Seems that this works - the DHCP obviously works, as does DNS, as I can connect via direct wired connection to the cable modem.

However, neither of these work via the router. New router (Belkin G) doesn't light up the "internet" light. Old router had similar woes. Operating systems windows & linux. Routers Belkin G and Linksys WRT54G. Patience thin.

posted by handee to Computers & Internet (8 answers total)

Best answer: My computer knowledge is extremely not vast, but I had a problem with my comcast cable modem a while ago, in that it would only connect to the internet with one of my computers plugged into it -- not my other computer, and not my router. I kept calling them and which computer worked kept switching. I finally noticed (though I should have noticed earlier), that when they reset the modem remotely, whichever computer was plugged in to it the time -- and only that computer -- then worked. I just had them reset it while my router was plugged in, and I get all my other connections through the router, and it works just fine. Perhaps try this, if it's possible?
posted by brainmouse at 10:01 AM on August 18, 2009

Best answer: The router (either one) may need to clone the MAC address of your computer, the one which you've previously plugged directly into the modem. You've fully reset both routers?
posted by now i'm piste at 10:03 AM on August 18, 2009

i know this is kind of dumb but.... bad ethernet cable? have you tried a different cable?
posted by geos at 10:04 AM on August 18, 2009

Best answer: Cable modems (certainly the NTL/Virgin set top boxes I've had in the past) are often MAC address specific. You can change the MAC address recorded in the modem as follows:

1) Switch off power to both the router and the cable modem. Wait a minute for them to discharge the capacitors.
2) Plug the router into the cable modem (if it isn't already).
3) Switch power back on to the modem and wait for it to connect (the lights stop blinking).
4) Now switch power back on to the router and wait for it to boot fully.
5) On computer, try to connect to any outside website: preferably using one of the wired ports. You should get some sort of setup screen asking for your subscriber number and password.
posted by Electric Dragon at 10:12 AM on August 18, 2009 [2 favorites]

(in 5, it may also Just Work rather than ask for subscriber details)
posted by Electric Dragon at 10:13 AM on August 18, 2009

Response by poster: Looks like a full reset of the cable modem then the router fixed it. I'd tried this with the old router, but not the new one:-) Guess the old one was b0rked anyway. Thanks Mefi! From problem to solution in 15 minutes.
posted by handee at 10:17 AM on August 18, 2009

Do you have to authenticate yourself to your internet provider? Your computer may be set up to do so and your router not. I often debug such problems by calling my provider and see what they think is happening on their end. E.g. if they want a particular MAC address, they should be able to tell you that they are refusing you for that reason.
posted by Obscure Reference at 2:37 PM on August 18, 2009

comcast DHCP lease is tied to mac address. If you change your router, you need to reboot the modem. You'll also get a new IP when you do this.
posted by cj_ at 3:00 PM on August 18, 2009