# Cable modem won't release MAC address



## Scops (Aug 28, 2009)

Hopefully, that title was descriptive enough to get someone's attention. I've been struggling with this guy all week, and this forum is a last resort.

The problem: My modem only works when I connect it directly to my primary PC. When I plug any other device in there is zero activity on the modem. I know that many cable modems seize the MAC address of the first device that is connected to it, and it appears that this modem, a Motorola SB5100 is one of those, but I cannot get it to _release_ the MAC address so that I can connect it to my router.

Background: I moved into this house a couple of months back, got Road Runner from Time Warner Cable, the 5100 was playing nice with the router, I could use my PC, laptop, and Xbox 360 at the same time, and all was well. Then a storm rolled through. Overpowered my cheap surge protector, and bricked the modem. Replaced it through Time Warner.

At first, nothing worked. Plugging directly into the PC would not even work. Then I called tech support, and tried to get things up while I had it plugged directly into my Laptop. When I mentioned I was running Ubuntu on said laptop, he kind of whimpered, so I played nice and plugged into my desktop, and voila, blinking activity light three seconds later. Since then, I've been stuck in the situation described above.

What I've tried: Swapping cables; swapping routers (I have two); cloning the MAC address to the router (no go); powering down the modem, waiting for 30 seconds (or 30 minutes, or 3 hours), disconnecting the ethernet connection, powering it back up, waiting for the status lights to stabilize, then connecting the router; resetting the routers to factory defaults; dialing into the modem and changing settings (unfortunately, I can only reset to factory or reboot); changing various settings on the router; plugging the laptop in instead of the PC (zero activity); plugging the 360 into the modem; moving the pc onto the DMZ while plugged into the router; most combinations of that which is listed above.

What I think: Three possibilities. 1)This modem is defective. Swap it out with TWC for free
2)The storm fried the WAN port. Plugging the modem into a LAN port does generate activity on the modem, but I've tried fiddling with the routing rules, to no avail. I doubt this is the issue, as the second router, which was unplugged during the storm, exhibits the same behavior.
3)Sometime before the storm, I dropped ZoneAlarm from my desktop, because it was playing hell with my PC, ran it without Windows Firewall for about a week (bad idea, I know), then got Comodo firewall. Somehow, maybe Comodo is causing my PC to play nice with the modem, when the other devices cannot.

Personally, I'm out of ideas, although I don't believe I've tried everything, as I would not be coming here. Does anyone think they can point me in the right direction?

Extra info: PC - Vista 32 sp1, Laptop - Ubuntu 9.04, Router 1 - TP-Link WR340GD Wireless, Router 2 - D-Link DI-524 Wireless. The PC and the laptop connect the routers wirelessly, although I have an extra long ethernet cable that I can use to connect directly to the modem from either one. The Xbox 360 is right next to the modem and router, so I connect that to the router with a wired connection.


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## ebackhus (Apr 21, 2005)

Those Surfboards are a PITA.

I work for Time Warner Cable and what you describing does sound a bit like a bad modem. Generally, resetting the modem while it's plugged into the new device will cause the modem to capture the MAC of that machine. If you are still unable to get it working try to swap it for an Ambit modem. Those have worked very well for me in the field.


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## Scops (Aug 28, 2009)

I started doubting myself in regards to the laptop, and sure enough, I remembered trying to tinker with to turn it into a WAP, and I forgot to set it back to DHCP. I tried it just now, and it worked. 360 does, too, although it is a new one (360 price drop, woohoo!).

My bad on the laptop, though I wonder if maybe somehow the storm fried the ethernet port on the old 360, in which case, I apologize to whatever poor soul buys it from that Gamestop. It would be a huge coincidence, though, and I'm a big fan of Occam's Razor.

So, it looks like it is reacquiring the MAC after a power off, but it is still not willing to touch either of my routers. I'd say it's a configuration issue, but both are sitting on factory defaults, and both worked in that state (or something very close to it) with my last modem.

ebackhus, thanks for the reply. With this new info, does your conclusion stand, or should I run some more tests? There's a retail location about twenty minutes from my house, so it won't take much effort to do a hardware swap, I just wouldn't be surprised if they grilled me about it, as it would be the second one in six days.


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## ebackhus (Apr 21, 2005)

Each time to move them modem to another device you need to power cycle it.


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## Scops (Aug 28, 2009)

Okay, so I traded modems (got an SB4200, grumble) the problem persists in its most recently discussed form, and now, whenever I get a transfer rate over, say, a half a meg per second (~500kbps), the connection drops. The activity light keeps blinking on the modem, but the computer behaves exactly as if I had it plugged in without synching the MAC Address ("There appears to be a problem with DNS," blahblahblah). This is with the computer plugged directly into the modem, btw.

At this point, I've swapped every component of the setup at least once, with the exception of the computers. I'm willing to accept the possibility that the routers are both bad, which is irritating, as the new one is juuuust outside of the store return window. While we're considering the less obvious possibilities, though, is it possible that the issue is at the street cable box? I don't know if any of my neighbors have cable, so i might be the only customer to complain. I'm wondering if I should just throw up the guise of a clueless customer (probably not as hard as I'd like to think) and request a site visit.


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## ebackhus (Apr 21, 2005)

Try swapping it for an AMBIT modem. Tiny little guys but are nearly flawless.


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## Scops (Aug 28, 2009)

Well, it turns out that both routers were bad after all. Coincidences suck.

It turns out that the issue with the 4200 isn't that it doesn't like connections over 500k, it just doesn't like parallel connections such as what is seen with torrents, or even with having too many browser windows open and requesting content simultaneously.

(End technical info here, begin consumer rant)

I went to see if I could get my 4200 swapped with something that didn't have this issue. I gave it to a TWC rep at a local storefront, she went in the back, and came out with a 4200 (same model), and I was disappointed, but willing to give it a try to see if the first one was just faulty.

As I was making the twenty minute drive back home, however, I noticed it had a smudge on the plastic, right about where the last one did. No, exactly where the last one did. The rep went into the back, came out with the exact same freaking modem, and just gave me a new power cable! When I asked her if she had a newer one available, she even had the gall to say, "No, and someone JUST dropped off this one." (her emphasis)

Of course, she said that if I had problems with this one, I couldn't return it, I would have to request a site visit from tech support. (Keep in mind I have three modem returns on my record in relatively short time at this point)

Tomorrow, I'm going to head to the next closest one (35 minute drive) and request another replacement, and raise holy consumer hell if they refuse. I'll also be sure to note the serial number this time before I drop off this crusty old piece of junk.

Sorry, not the place for this, but grr at TWC-NC. Maybe the storefront tomorrow will have an Ambit modem.


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