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MikeD · Jan 23, 2004, 04:21 PM

For those who have Comcast Cable Broadband, does it use DHCP and do you need to provide a login/password to access the network? My in laws have a cable modem and all of a sudden, it stopped working. I wasn't sure if it was anything like my DSL service that uses PPOE and I have to provide my login/password (in my router) to access the net. Anyone have any insight into this so I can help them out?

Thanks,
Mike

Chris_G · Jan 23, 2004, 04:36 PM

Originally posted by MikeD:
For those who have Comcast Cable Broadband, does it use DHCP and do you need to provide a login/password to access the network? My in laws have a cable modem and all of a sudden, it stopped working. I wasn't sure if it was anything like my DSL service that uses PPOE and I have to provide my login/password (in my router) to access the net. Anyone have any insight into this so I can help them out?

Thanks,
Mike

It uses DHCP and you do not need a login/password to access the network AFAIK (current ATTBI/Comcast subscriber).

Chris

MikeD · Jan 23, 2004, 05:51 PM

So all you have to do is plug the ethernet cable in and setup your computer (They have this windows me stuff) to accept DHCP and it should all be okay?

Mike

ghporter · Jan 23, 2004, 09:51 PM

Actually, it probably uses DOCSIS, rather than DHCP-it's a cable-specific standard that includes two-way management communication between the modem and the network.

And your in-laws' problem could be that they're using Windows ME (not bashing, it's just a really bad OS).

Cable newtork connections are more sensitive than TV connections, so a bad connection somewhere could kill their Internet. Have them/help them check every cable connector to make sure they're all tight and the cable is secure in the connector. Also, make sure the outside part of the cabling is OK.

tooki · Jan 23, 2004, 10:16 PM

Be sure to try resetting the cable modem: turn off/disconnect power from the cable modem. Disconnect the ethernet cable to the computer. Turn on/plug power back into cable modem. Reconnect ethernet.

tooki

MikeD · Jan 23, 2004, 11:28 PM

Thanks everyone for your advice... Sheesh, should I even help them for them getting a windows and not a mac in the first place?!

BTW, unlike my DSL modem, theirs is this weird RCA that blinks randomly each time. Sometimes it's two lights that blink on and off in a pattern (I think it's internet and PCLINK but I'm not there right now so I can't confirm) and other times it's just other lights going off. Not your typical on off switch either. Do I need anything else driver wise or do I just set TCP/IP to DHCP and get everything automatically?

Thanks again,
Mike

John Strung · Jan 23, 2004, 11:33 PM

Just set TCP/IP to DHCP and everything should work.

oscar · Jan 24, 2004, 04:10 AM

You need to run the setup utility, and give comcast your MAC address, that could be the problem

ghporter · Jan 24, 2004, 09:58 AM

Oscar brings up an important point that needs a little expanding.

Most cable systems authenticate their users by having the modem check the hardware address, called the MAC address, of the network device that's connected to the modem. While this keeps the user from having to log in to connect, it also allows the cable provider to enforce an "only one computer connected to the modem" policy. This is why people buy cable/DSL routers-they can be set to give a cable modem whatever MAC address you want.

If a cable modem experiences a power glitch or just gets stupid, it can forget how to work, or forget which MAC address has been authorized by the cable provider. If the reset that Tooki described above doesn't fix the problem, you should call Comcast's tech support. They can reset the authorized MAC address, or tell you if there's a hardware problem somewhere.

To get the MAC address on a Windows computer, open a command line window and type "ipconfig" without the quotes. A MAC address is a group of six pairs of hex characters (0-9 and a-f or A-F). WinME may not support ipconfig. If so, open the Start menu, click on Run and type "winipconfig" without the quotes.

MikeD · Jan 24, 2004, 10:35 AM

And for that MAC address, whenever you get it, you would program the router with it in the section (This is for a linksys router) "User definable WAN MAC address"? I found it under the advanced options of my router (They have a similar router). But since I have DSL, I just use the PPOE with login/password...

By the way, in the router settings, besides setting up that MAC address thing up, I would setup the connection to simply obtain an IP automatically right? Not PPOE or any of the other options right?

Mike

ghporter · Jan 24, 2004, 10:36 AM

You got it! That's it exactly.

John Strung · 11:45 AM

"IPConFig" works to get the MAC address on WinNT, 2000 or XP. For Win95,98 or ME, the instruction is "WinIPCfg" (not case sensitive - type "WINIPCFG"). Make sure you switch from your PPP connection to your ethernet connection using the popup menu.

On WinNT, 2000 and XP, if you have more than one network interface (e.g. wired and wireless cards) use "IPCONFIG /ALL"

MikeD · Jan 24, 2004, 01:08 PM

Would this work (Getting the correct MAC address) if the internet currently isn't working on the computer? Or can this only give the correct response if you're actively connected to the internet (Therefore connection between computer and Cable modem is positive)?

Mike

ghporter · Jan 24, 2004, 01:24 PM

If the problem is that the modem doesn't know what MAC to look at, resetting it should fix the problem. If it doesn't, then call tech support.

MikeD · Jan 24, 2004, 02:31 PM

Okay will try and post whatever happens.. Thanks!

Mike

stevesnj · Jan 25, 2004, 08:56 PM

GET RID OF THAT RCA MODEM!!! I fix computers on the side and when my customers have connection problems it's always with an RCA cable modem. Just go to your local Comcast Equipment/payment center and exchange it for a different modem, preferebly a Motorola.

-Q- · Jan 26, 2004, 01:42 PM

I know when I had comcast cable internet installed here in Atlanta, the technician told me access to the network was controlled by the MAC address of the cable modem. They didn't seem to care what was connected on the other side of the modem so long as the modem that was assigned to your account was used to access their network.

tooki · Jan 26, 2004, 08:06 PM

I was just gonna say...

The modem has a MAC address, which is what Comcast needs to know. They do NOT need to know the MAC address of your computer or router (they stopped using MAC address authentication years ago).

However, the cable modem does enforce MAC address limits: the first computer (or router) to communicate with it after initialization is the one that it will then work with (or the first X devices to communicate with it, if you have paid for multiple IPs).

Here's a super-simplified, inaccurate-in-fact-but-accurate-in-concept description of how DOCSIS cable modem systems work:

(During installation, the cable company is given the modem's MAC address, so they know that that modem is for your account.)

1) Modem powers on, and sends out a "Hi, I'm here!" message to the cable company
2) the cable company's DOCSIS server sends a configuration file (tagged with the cable modem MAC address) out onto the network, and your cable modem listens for it.
3) cable modem reads the configuration file, which tells it whether to perform NAT, DHCP, etc, what its IP is, how many clients to allow (by MAC address... any clients over the allowed number are simply ignored), what speeds to allow, etc. and sets itself up accordingly (by the way, it is possible, albeit very difficult, to spoof the DOCSIS server and send your own configuration file; people have done this to steal tons of bandwidth)
4) The connection is now up.

tooki

ghporter · Jan 26, 2004, 09:29 PM

Originally posted by tooki:
I was just gonna say...However, the cable modem does enforce MAC address limits: the first computer (or router) to communicate with it after initialization is the one that it will then work with (or the first X devices to communicate with it, if you have paid for multiple IPs).

Extremely well said. It's a distinction I had kind of blurred over, but an important one. There are still cable systems that worry about your computer's MAC address, but you usually know when you use them because they tell you how to add or change computers. Some cable systems also seem to control when the modem accepts new addresses, as well. They're the sneaky ones...

MikeD · Jan 26, 2004, 09:49 PM

So then, if this modem is connected (From Comcast) and is only connected to one PC, why is it still not working then? Because of this, is there something special / different we need to do to get the router hooked up? Or is it still a matter of getting the cable modems MAC address programmed into the router?

Mike

ghporter · Jan 27, 2004, 05:08 PM

Check with their tech support. One computer on THEIR modem should either be working or have a trouble ticket on it.