Sunday, September 17, 2006

time warner and routers

A friend asked me to set up a router to work with his Time Warner cable modem. The symptoms were confusing: if you plugged his PC into the cable modem directly, the cable modem would give it an IP address and everything was happy. If you plugged the router into the cable modem, there was a link light but nothing else.

After a couple unhelpful tech support calls, during which T-W's techs repeatedly told me I'd have to call the router manufacturer, despite my patient explanations that the router manufacturer wouldn't know diddly-squat about how T-W set up its network, a Google search got to the bottom of it: Time Warner is filtering by MAC address.

You see, every Ethernet device in the world has a unique serial number, called a MAC address. When the Time Warner tech set up my friend's cable connection, he must've configured the cable modem so it would answer to the Ethernet jack on the back of my friend's laptop--and only to that Ethernet jack. Because of the way T-W set up their cable modem, if my friend had to replace the laptop, or decided to plug in a desktop machine instead, or bought a PC-Card Ethernet card and plugged that in, or plugged in a router, the cable modem wouldn't deign to talk to it because it would have a different MAC address. Of course, none of the techs mentioned anything about this limitation when we talked to them, even after the Google search when my friend was pressing them about whether there was any sort of filter in the modem.

Anyway, the work-around is easy: newer routers, like the Linksys WRT54G, have a feature called "MAC address cloning." The router can change its Ethernet's MAC address to match whatever one your PC uses. Clone the MAC address and suddenly the cable modem is friends with your router.

Of course, it's up to you whether you want to do business with a company that goes to such lengths to make it hard to use the service it's purportedly selling you. Personally, I have DSL with one of T-W's competitors.

4 comments:

Paul TS Lee said...

Hmmm, you could also try and leave the cable modem's power unplugged for a whole minute, then plug in the router (also power off), then power up the modem, and finally the router.

I'm guessing that unless a TW tech set the modem up and somehow configured it with the computer's MAC address, the modem just grabs the address of the first device it sees, which would've been the computer (via USB, I'll further hazard). The modem probably caches that address, which ought to be cleared once it is completely unpowered for a bit.

I don't see how TW could configure their modems to filter out the MAC addresses of all device manufacterers, and why they'd bother in light of the fact that pretty much all current routers can "spoof" some other MAC address.

Anyhoo, good luck.

False Data said...

I'm not sure how the tech programmed the modem, but by the time I got there the only connection between modem and laptop was Ethernet.

As for powering off the modem, I don't know whether or not it'd work. It's possible it just snaggs the first MAC it sees on the line. It's just as likely it uses battery-backed CMOS to hold onto configuration settings.

I think it does make economic sense for them to configure their modems to filter MACs because (a) it's cheap for them to do it, and (b) it allows a degree of price discrimination. Most of their users have no idea what a MAC address is or why one should want to spoof one. Even those who know might have no idea it's necessary in this case, especially if the responses we got from tech support are typical. Unless those users have a friend who's spent a fair bit of time learning the technology or are among the (few) readers of certain relevant blogs, they'll be limited to one machine on the network. If they want more, presumably TW will be happy to sell them a router and have a tech reconfigure the modem.

mad said...

because they are no good jew fucks

Anonymous said...

After paying a ton of money to Linksys tech support, the representative told me Time Warner's cable modem could not give me an IP address when I plug my laptop directly into the TW Cable Modem. After I insisted on doing an ipconfig /renew command to the techs surprise I got a new IP address. Then I was instructed to plug my laptop back into the router, the router back into the modem and power cycle modem and router. Now back to the original reason I called Linksys, I could not get an IP address. If I would just pay another $50.00 more than what I have already paid they would be able to help me. When I baulked at this the tech began to tell me all the things they could do for me. One being clone the mac address and if that didn't work, refresh the router. What she meant was factory reset the router. Just to let you know nothing they did worked at all. After weeks of going back and forth with Linksys I purchased another router... My mistake was I purchased another Linksys router.