I’d just like to note that I have had the same comcast IP address for years at a time — the longest being about 3 years, with several 1 and 2 year stints. (I wanted this for remote control reasons.) You do this by hooking up the modem to a UPS. I even moved 10 miles and kept the same IP. I just kept the modem connected to the UPS in transit, connected it to the cable at the new house and everything worked fine. I was amazed because you’d think it would be a different node 10 miles away that would not allow an other node’s IP address. (I even went from 6 Mbps to 15 Mbps probably because it was a new development with new cable, repeaters, etc.) I think this shows the absolute key to getting a new IP is turning off the modem.

For example, the UPS died a few months ago (unbeknownst to me), and there was power outage for 5 minutes and boom! — a new IP address even with the same MAC address from the router. So just keep trying — in my experience anytime the modem is off for more than a minute or two (there is some “stickiness” for very short time periods), you get a new IP. So just keep experimenting and don’t rush and you should get a new IP address in short order. Good Luck!

I suppose I’ll have to call Comcast and ask politely for a new IP.

I looked all through it and found the password/username for the default Time Warner setup. The password is different for Comcast but wow, what a security hole they have up there on the web

So I just got off the phone with them. The problem is definitely that I have business class service and the modem/router (SMC8014WG) does not seem to allow for changes in the mac address. The solution is going to be dropping to residential service so I can provision my own router/modem. Apparently that’s not an option for business class people.

How strange.

As far as compatibility questions as to DOCSIS 3.0 vs DOCSIS 2.0 it is important to note that the forum folks talk about the SURFboard SB6120 Cable Modem, though the article was written a while back. On the other hand, I imagine that Amazon has a number of reviews and comments that would be helpful to read over when trying to select your ultimate new modem.

I read that very article last night. It’s actually a bit confusing with the one poster reversing his position “it definitely will not work with dynamic, er I mean static”. LOL.

So then you and I agree it’s time to find a DOCSIS 3.0 capable cable modem, one where I can clone the mac.

I found a linksys cable modem on craigslist for $10, let’s see if this solves the issue

Here’s an interesting post:
http://www.dslreports.com/forum/r21985378-Buying-a-DOCSIS-3-Compliant-Cable-Modem

“Cable Modem manufacturers are utilizing practices that restrict your ability as a consumer to choose. ALL, I said ALL of the major manufacturers of DOCSIS 3 cable modems will only sell exclusively with multisystem system operators (MSO’s) aka your “cable company” and cut out consumers. So far I have found that NETGEAR, MOTOROLA, CISCO (Scientific-Atlanta) and SMC all have DOCSIS 3.0 cable modem equipment available, but are only selling exclusively to MSO’s. I know this because I’ve called all of them and asked them! Some of these companies have gotten angry and upset that I’ve asked them about this question.

These new modems have been out for some time (Cisco has had theirs out since at least March 2008) and you still cannot buy one.”

Oh, and thanks for the manual for the SMC. Yes that’s it. Main problem with it is it’s been modified and runs a ‘comcast’ web interface, not the “standard” web interface. The ip address of the modem is 10.1.10.1, in the manual they talk about using 192.168.0.1

The problem I’m having now is finding a docsis 3.0 cable modem. Think I can use a docsis 2.0? (They are easier to find).

The Comcast modem and the router that you have are integrated together in one hardware unit, and is apparently lacking the ability to clone MAC addresses.

I believe you have the following Comcast modem/router SMC8014-BIZ. Download the manual from the SMC website. The SMC website search is located here.

If I understand your hardware setup properly, you are using another router on the output from the built in router of the Comcast modem/router unit. If that is indeed the setup, the separate Linksys router, WRT54G, is simply acting as another device on one of the output port lines on the Comcast modem/router unit. Because of this setup, you are not changing the MAC address at the source. You are only changing the MAC address of the Linksys router if you clone a MAC address on the Linksys router itself.

Now, for the solution to your dilemma and the answer to your question if you can try a different cable modem. I found a very very informative forum talking specifically about Comcast Business Class and more specifically about using a different modem other than the modem supplied by Comcast. Broadband Reports has a topic titled, [Business] Does Comcast Business still allow non-SMC modems? The forum article thread covers the topic extremely well from start to finish about adding a different modem to Comcast Business Class. Apparently, the simple answer is, yes you can install a different modem on Comcast Business Class. However, there is a bit more to the process than meets the eye. I suggest reading the forum thread carefully from start to finish.

By the way, here is a comment on the forum that supports the analysis presented here: “So long as your MAC address (attached to the modem, or the modem itself) doesn’t change, you’ll pretty much keep the same IP for quite a long time.”

I’m thinking Comcast is using the mac address of their comcast/smc “gateway” modem to set the ip. I have some access to the modem through the web admin panel, but the modem does not allow mac address changes/cloning.

I cleared my arp and then ran:
arp -a

before rebooting the smc modem I get
192.168.1.1 xx.xx.xx.e4 (I thought I expected to see the cloned mac here and I do not)

I don’t know if I should be seeing something else, not sure what you see on your linksys (mine’s a wrt54g). I notice, fwiw, that under:
status -> router
my cloned mac address appears

status -> local network
sames as arp query result;
192.168.1.1 xx.xx.xx.e4

status -> wireless
xx.xx.xx.e6 (same prefix as local network)

Can I try a different cable modem?

If it is really a dynamic IP, then it is possible that the IP address is not based on the MAC address at the user’s end, and could simply be targeting the MAC address of the modem. Maybe they figure it more likely that in Business class setup, that the business customer would be adding a router and many other computers, and therefore business customers are less likely to maintain the same attached computer directly to the modem and Comcast doesn’t want the system to keep reassigning IP addresses for that reason.

Or, if you somehow got a static IP address that was assigned to you by Comcast, and you simply can not change it because it is fixed.

They assigned a ‘dynamic’ ip address the day i started and i can’t get it to change for the life of me.

I have an SMC business gateway cable modem which allocates dynamic addresses (dhcp) within the dmz at 10.1.10.1 addresses.

I started with a single computer in the dmz and tried to change it’s mac, but that’s pretty hard. So I bought a wrt54g and placed it between my laptop and the smc cable modem. I changed the mac address by using it’s original and two cloned macs.

Still, i have the same ip address. I cannot get it to change.

Any thoughts?

There are a couple of clarification points here to consider.

Most devices, probably including the modem itself, have MAC addresses. A Media Access Control address (MAC address) is a unique identifier assigned to network interfaces for communications on the physical network segment. MAC addresses are used for numerous network technologies and most IEEE 802 network technologies including Ethernet. Logically, MAC addresses are used in the Media Access Control protocol sub-layer of the OSI reference model.

I say above, probably including the modem itself, has a MAC address, though I am not absolutely sure on that one. However, I do know, that the modem itself is registered with Comcast, with some unique identifier, which is tied to a particular physical address location. Now, the way the Comcast DHCP server assigns IP addresses seems to be dependent on the end user’s MAC address of either a computer hooked up to the cable modem, or an attached router assigned MAC address, which triggers the Comcast DHCP network server to assign an IP address. This IP address seems to be assigned in a lease arraignment, relative to the MAC address and the cable modem. On receiving a valid request, the server assigns the computer an IP address, a lease (length of time the allocation is valid), and other IP configuration parameters, such as the subnet mask and the default gateway. In essence, I suspect Comcast keeps track of all the IP addresses that have been assigned to the particular cable modem, and the dates of when those IP addresses were assigned.

So, what happens when you assign a new MAC address, the DHCP server at Comcast assigns a new IP address. Sometimes, if you switch back to the old MAC address, before the IP lease is up, and before the IP address is reassigned to someone else, the DHCP server at Comcast will reassign the old IP address to you.

So, the bottom line is, in my opinion, there are cross-reference times, MAC addresses, and IP addresses that can track you online no matter what. It all depends on how long Comcast or any other internet service provider keeps this information on hand. The information would have to be subpoenaed though.

Many Thanks

You saved me hours of grief. Keep up the good work!

So for saving my head another headache and from saving my eyes from another “Call Comcast to reset your IP” I have to thank you again ^^

Hope all is going well for you =D

First I called comcast a couple times and asked if they would reset it. They reset the modem but the ip remained the same.

Then I hooked the modem directly to a laptop instead of thru a router and got a new ip address. When I plugged the modem back into the router it registered with the orignal ip address.

At that point I followed the instructions. Entered in made up numbers in the mac clone blanks and released, renewed, reset the modem, release & renewed again and then had a totally different ip.