Unshackle my home network
October 20, 2006 7:27 AM   Subscribe

Linksys WRT54G Wireless Router + Comcast Broadband connection. My Comcast connection will not allow the internet to flow through the wireless router

I've seen on a few websites that you must reset the IP address in order to "fool" the Comcast modem that your router is a PC, but my wireless illiteracy or the explanations I have found are holding me back.

Explanations at the level of "See Jane Run" or in Seussian rhyme preferred.
posted by MasonDixon to Computers & Internet (14 answers total)
You can use a feature called "MAC cloning" -- on a Windows PC, run the ipconfig command in a DOS window and jot down the MAC address of your network cade.

Next, log into the web interface of the router and find the "MAC Address Clone" tab in the Setup Menu. Enter the MAC address you jotted down from your PC. Save your changes and exit the control interface.

I hope that's easy enough of an explanation.
posted by briank at 7:31 AM on October 20, 2006

cade= card
posted by briank at 7:31 AM on October 20, 2006

Have you tried unplugging the power from your cable modem, then plugging it back in?
posted by rbs at 7:31 AM on October 20, 2006

You have to turn on MAC Address cloning
posted by bitdamaged at 7:32 AM on October 20, 2006

Like everyone else said, use MAC address cloning. You are gonna want:

ipconfig /all

to get your MAC from a windows command prompt. It will be listed as the "Physical Address" and look like xx-xx-xx-xx-xx-xx
posted by blind.wombat at 7:51 AM on October 20, 2006

how have you determined that the problem is with comcast? in my neck of the woods they did away with registering mac address several years ago.

when you connect to your router what ip address is assigned to your computer?
an address like 192.168.1.xx indicates that your computer is connected to your router and leasing an ip address from it.

as others have mentioned you can check this by typing ipconfig.
posted by phil at 8:27 AM on October 20, 2006

an amendment to my previous post. if you do not see an ip address formatted like 192.168.1.xx you have a problem with the way your computer is hooked up to the router, not with the way your router is connected to your isp.

also page 46 of the router's manual covers mac address cloning.
posted by phil at 8:38 AM on October 20, 2006

I have Comcast and there is no need to clone the MAC for me, despite changing routers, hooking the computer directly to the modem, hooking a different computer directly to the modem, etc. If the router is talking properly to your computer, I would give Comcast technical service a call. I had an issue and they sent someone out (for free) to check the lines, and he ended up giving me a new modem. I am pretty sure that Comcast expects that many of its customers will be setting up a wireless router and does not have a policy against this.
posted by caddis at 8:57 AM on October 20, 2006

Have you tried unplugging the power from your cable modem, then plugging it back in?

Yep, generally, the cable modem "binds" to the first mac address it sees upon power up. So if you have it working directly with the PC, you'll need to restart the cable modem after hooking it to the router. Common mistake.

The default Linksys settings should be okay to get started, but if it still doesn't work, bribe a geek to help out with the DHCP settings and such.
posted by LordSludge at 10:27 AM on October 20, 2006

We have Comcast, and we connect the Comcast cable modem directly to a Linksys wireless router and it works fine without having to mess with any settings.

On occasion, the whole setup needs to be rebooted (shut everything off, reboot), but then it is fine.

I'd second the suggestion that you try to eliminate a hardware problem:

1. Does the cable modem work when it is connected directly to your computer? If so, then your cable modem seems fine.

2. Can you borrow another wireless router to test out the connection? Or can you lend your wireless router to a friend who could test it out for you?
posted by jerryg99 at 10:39 AM on October 20, 2006

Best answer: I have recently been through extensive problems with this very router, a modem, Comcast service, and Linksys support, and let me offer the following suggestion: before you waste any more time, please consider pressing reset on the modem and the router, unlugging and unconnecting everything, waiting a bit, and then setting up the wireless network anew per the setup protocol. In my experience, this was the only thing that did the trick of wiping out the address preferences and blocks, which seem to be stored in the devices. This resolved a different situation that had flummoxed tech support, and might work for you. FWIW, I did not have, and still do not have, cloning enabled, so while that may be a solution it was not necessary in my case.
posted by Clyde Mnestra at 10:55 AM on October 20, 2006

Yep, Clyde nailed it. Push the reset button on the back of the modem in with a pen.... then reboot windows.

If that does not work then reset the router and then reset the modem. (and obviously reset your security configurations back on the router)
posted by Slenny at 1:30 PM on October 20, 2006

I have Comcast cable, a Linksys WRT 54G v3, and several Windows and Linux boxes behind it. Let me explain/recommend a few things unmentioned by others so far in this thread.

1) If your Linksys router firmware has not been updated to the latest revision, do that, through a wired Ethernet connection, before proceeding. Early versions of Linksys firmware had some bugs that affected interoperation with DOCSIS systems like Comcast. You'll need to refer to the sticker on the bottom of your unit for its actual hardware version, and choose the matching download on the Linksys site. You can check your current software version in the Linksys Administration interface, by going to and logging in using the default credentials, or whatever user name/password you set up when you first logged in. For late version of the firmware, the version number is in the upper right hand corner of the admin interface pages. Mine is currently 4.30.5, the current version as of May 2006.

2) It's not clear from your question whether or not you've successfully connected via this modem from your current location to the Comcast network. If not, you do have to go through a registration procedure with Comcast, and they will care about your modem's MAC address during this procedure (which they will autosense over the cable network, and use to populate a table on their configuration servers with the name and service address you supply). If you change or replace your modem, or move to a new service address, you will have to go through the registration procedure again, to put the new modem's MAC address into the Comcast configuration table. This is how Comcast knows you are a "legitimate" customer when your cable modem powers up, and tries to login to their network, and "spoofing" the address with an older modem's MAC address won't work. If your modem isn't "recognized," by the Comcast authentication server, you never get a valid IP address assignment on their network, and you can't do anything. You can't have your Linksys router in line while doing the sign up procedure, because you won't be given routable addresses until the sign up is over. So, if you haven't successfully completed the self-install or had a Comcast guy do your install, finish that first, before trying to hook up your Linksys.

3) You need to understand Dynamic Host Control Protocol (DHCP) a little bit, to understand how to connect and use your router on a cable modem network. Your cable modem has a DHCP client on its cable facing side, and an internal DHCP server on its ethernet port. The standard configuration of the cable modem is a little weird though, in that it will hand out a DHCP address of something like initially on power up, on the Ethernet port, and then in 30 seconds to 2 minutes, when it has successfully connected to the Comcast cable network, and its own DHCP client has obtained a valid IP address from Comcast, it will change the addresses it is handing out via its DHCP server to the address, gateway, and DNS server information it got from Comcast. [That may sound like convuluted gobbledegook, but having the DHCP server pop up on a stock address as soon as it is powered up is useful, if you need to login to the modem from the client side to watch it's internal status reports as it is connecting to the cable network.] So, you need to fire up the cable modem a couple of minutes ahead of your Linksys router, to be sure the cable modem has had time to get a valid address, so that the Linksys isn't working with a non-routable private IP address it got from the cable modem's internal server. You can check this in the Linksys administration interface, by looking at the Status page, and seeing if the public address and DNS servers look like "real" IP addresses. Anything starting with 192, 172, 169, or 10 are non-routing "private network" addresses, and you'll need to figure out why your cable modem isn't getting a real address to the Linksys. At that point, Comcast support should be able to look directly "into" your cable modem on its internal Web server's interface, and see exactly what is going on with their network, from your modem's perspective. They can't "see" into your network, behind the Linksys, if you are running the default firewall on your Linksys. If they say they can see a valid IP address given to the cable modem, unplug your Linksys, wait a couple of minutes, and plug it in again, to let the DHCP client in the Linksys grab the "real" IP address from the Comcast modem.

4) Once the Linksys has a real IP address for its uplink port, it should also have a gateway address, and DNS servers to point at, on the Comcast network. If you can log into the Linksys from your Windows box, you should be able to ping those DNS servers. Type ipconfig /all at a WinXP command line, and make a note of the DNS servers listed. Type ping XXX.XXX.XXX.XXX where XXX.XXX.XXX.XXX is the IP address of a DNS server, and you should demonstrate that you can successfully route packets from your laptop to these servers on the Comcast network, using IP protocol. You can also type something like ping www.microsoft.com and see that the DNS servers at Comcast resolve this name query, and send your machine back a valid address for www.microsoft.com that your ping command can then use automatically in its ping test.

If you can't do 4 successfully, but Comcast says they can see into your modem, and everything looks good to them, they'll want you to eliminate the Linksys router, and use only 1 Windows machine directly connected to the modem to demonstrate that you can get packets through the cable modem. That's fair on their part, and doesn't indicate that your Linksys won't work, only that it might have a borked setup. So do that with them, and if that works, but you still can't connect through the Linksys, post back here with the exact output of the ipconfig /all command you get when the Linksys is in your loop, and we'll try to see what's wrong.
posted by paulsc at 1:32 PM on October 20, 2006

Response by poster: Thanks to everyone.

What I ended up doing was disconnecting the ethernet cable from the computer, while disconnected I held down reset on the router for several seconds; hit "standby" on my cable modem and then held down its reset button.

I then killed the power to router, modem and PC. I even disconnected the modem from the broadband cable.

After fifteen minutes, I hooked the modem cable to the router and the router to the PC. I reconnected the broadband cable to the back of the modem, powered everything back up, switched the modem off "standby" and now everything works perfectly.
posted by MasonDixon at 10:04 PM on October 22, 2006

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