New Computer on RCA Broadband Modem & Comcast

Dec 09, 2004 14 Replies

Hi All,



I brought home a new laptop today and tried to get internet out of my RCA broadband modem.



The laptop does not get an IP address out of the modem (DHCP lookup times out).



I thought that once the modem is provisioned (Comcast knows the MAC address of the modem) it shouldn't matter what computer is plugged into it.



Does the modem look for the MAC address of the NIC in the computer it is attached to?



Help appreciated,



Matt


The cable modem will likely only recognize one computer. Depending on your cable company, you may be able to release dhcp in the old computer, before disconnecting it and then boot up the new one, after connecting it. With some companies, you may have to call the help line. Another and better way, is to get one of those cheap firewall/router boxes, and have it clone the mac address from the original computer. This way, you can have both computers connected and you greatly increase your computer security.

Yes, the MAC it saw during powerup. Power down cablem modem, wait 15 sec by your watch, and power up. No connection, release/renew your laptop connection.

Yes.

And, although it's been posted a gazillion times in this group, some suggestions are worth repeating: GET A ROUTER AND THIS WILL NEVER HAPPEN TO YOU AGAIN. The router's MAC becomes the MAC the cable modem sees and thus you can switch out items behind the router as often as you like and your modem will happily putter along.

Comcast never cared if I was swapping computers around. I was even using one on the USB and one on the RJ45. Whichever was on when the modem came up was the one it used. I swapped the RJ45 between a PC and an RTV. Finally all the swapping got to me and I got a router.

I've changed routers a couple of times & never had a problem. When Comcast provided a new modem & the installer did self-provisioning directly from the computer, then I had to tell the router to use the computer's mac addr.

Probably should have done self-provisioning myself thru the router if possible.

There are a couple of things to consider here. When both Comcast and ATTBI first left @Home, to cut down on the number of support calls, they set everyone's modem to allow for a bunch of devices to be attached to each account. Once things stabilized, they reset the maximum number to match the maximum number that people were paying for. So after that, people not paying for multiple IP addresses could only connect one device at a time.

However, even if you're only allowed to connect one device at a time, power-cycling the modem will allow you to change what device you have attached to it. It's just that simple!

The cable modem should work with any computer he connects to it, so long as it has DHCP enabled. Even an Apple for that matter.

Bill Crocker

They don't do this in Michigan.

Bill Crocker

Hook the modem to your new machine while the laptop is on. Power cycle the modem. You should get on fine

Be aware that several modems just recently became obsolete on the Comcast system in this area. Any modems that do not support DOCSIS 1.1 won't work any more. These include older surfboards (3100 and down), RCA DCM215, 315, old com21 (DXP111), and a few others.

I was helping someone get their linux box running on cable and we found we had to cick up a cmd window and do a ipconfig /release before swaping hardware connected to the cable modem and doing the cable modem power reset.

The computer can't get a valid IP address until *after* the modem has been power-cycled. If you turn on the computer before power-cycling the modem, you will have to wait until either the non-routable IP address it gets expires, or you have to manually release/renew.

The two problems with this are, 1. People usually don't have the patience to wait for the computer to attempt an automatic renewal, and

  1. People have a tendency to want to "renew ALL" (instead of just "renew" for the Ethernet adaptor only), which also forces the dial-up adaptor to attempt to renew an IP address using the dial-up modem, leading to an error message.

The work-around to all of this is to power-cycle the modem while the computer is off. Once the modem has sync'd, connect and boot the computer. It will request an IP address. It will get one. Problems avoided.

The same if you have a router between the computer and the modem. Start with the modem. Then the router. Then the computer. It's not impossible to have success not doing it 1-2-3, but the conditions must be just right, and you may need to perform additional actions that essentially put things back in order. If you just do 1-2-3 in order, you don't have to worry about all those side issues that could get in the way.

The modem will lock itself to the first mac address it sees...the way

around this is to pull the power cord on the modem, then plug it back

in (with the modem hooked up to the laptop, of course)...this will

allow you to pull an ip address with laptop.

Hope this helps :)

I'm curious, what would happen if you tried to use one of these "obsolete" modems that don't support docsis 1.1 now on Comcast? Nothing at all? unpredictable?

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