I have Comcast as my ISP (Cable with static IP) and I noticed that my IP address changed from starting with a 24. to 67.

At the sametime, I've noticed that most, if not all the spam I report for Comcast comes from IPs starting with 24.

I'm wondering why the change? Anyone know if changing IPs are a common practice with ISPs?

...Don't know for certain but it would not at all surprise me. They could presumably hard-code an IP address for each customer but that would be rather expensive. Instead, they might use a dynamic IP address assignment. They might even provide "affinity" -- once the automated mechanism assigns you an IP address, it will keep that IP address associated with your machine until you become inactive for, say, 10 days, then they might reassign it to another (new?) customer and assign you a new one when you come back in.

that could be the case, but I use my machine and have had the same IP for the past 2 years. I thought it was odd that it's never changed until now, when there's been no change to my usage. I use my connection everyday, so I just don't know what would have prompted the change.

...Have you tried the Comcast Help page?

Just as I thought.

You have been lucky to maintain the same IP for a long time but unless you have a busine$$ account or a home account and pay additional for a $tatic IP then it is dynamic.

...From original post:

He did not say he paid for a static IP, he might have thought he had a static IP.

This is from the Comcast site:



Maybe I'm a tad confused... I thought dynamic meant it changed, like dial-up? My IP has remained the same and I've never paid extra for that. Am I misinformed about static/dynamic or have I just been fortunate to get the same IP for such a long time? Also, if they're dynamic, why is the IP address the same everyday?

They will stay the same if you stay online, or are only offline for short periods. You get a lease, and the last time I checked it was a couple of days. The only time I've lost my IP in the last several years has been when I shut everything down for VC, and when Comcast merged with AT&T.

I now keep my router on all the time, complete with its own UPS.

Static = it's "you" until you do't pay the bill

Dynamic - it's the toss of the coin

Going back to the modem days, ans ISP might have 200 customers and is able to keep all 200 of them happy with only 80 actual phone lines coming in. How/Why? Because not everyone is on-line at the same time, not all stay on-line for a great length of time .... when the complaints of "always busy" come in, then more phone lines are needed.

These days, with the high-speed stuff, it's kind of the same issue, just scaled up a bit. Instead of worrying about the numbers of phone lines, now it's the number of IP addresses the ISP controls. This is where the difference in "dynamic" and "ststic" comes inot play and why they charge more for the static ... just as in the modem days, if "you" weren't using the "line" .. that line could be given to the next "caller" .. thus allowing service to more customers than "lines" available. Assigning a "static" IP to someone removes it from the pool.

There is some time delay built into the modem/router/switch/etc. configuration to handle the occasional drop-out, missed packet, etc. And there's the "lease" time alloted to a connection to keep that set of boxes from going "on the hunt" if you drop your connection for any reason. If you're connected "all the time" then the lease time may come up dor renewal, and their system simply "renews" the existing lease. So you march merrily along.

One of the funny scenarios is calling for help with problems with a cable-modem connection. One of the first scripted steps is to have the customer unplug their modem and let it set for 15 to 30 minutes. It's not that the modem needs that much time to clear out/reset/ whatever ... it's more shooting for the existing lease to expire and a "new" connection is made at the next connection, thus possibly "routing around" a possible real failure point. Very similar to the old days of mechanical switches involved in the POTS (plain old telephone system) .. 99% of the "failures" were due to dirt/corrosion/tarnish on the switch contacts, but this data was not to be provided to the customer. So the "procedures" were for the tech to arrive at site, find the switch, clean all the contacts, replace the covers, then attempt to address the customer's "problems" .. which of course ususally had disappeared for some reason <g>

I can relate that I had one IP for almost two years. Then went through a dozen different IPs over the next few months. The one I'm on now is less than two weeks old (to me) .... Why yours went from a "12." to a "67." can only be answered by someone in the ComCast networking office .. but remember that ComCast has been buying/merging/picking up other stuff all the time ....

Maybe that's why. I leave my cable modem on all the time, even when my computer is off (because it's on the other side of my apartment). The only time I've ever turned off the modem is when I needed to power cycle it.

It will not make a difference if you turn it off or not if your ISP decides to change it.

The DHCP assignment is a lease that contains an expiration time. As the lease gets close to the expiration time, the leasee can request renewal. The renewal request will first go to the DHCP server that the lease was obtained from. If it is not able to get a renewal, it will broadcast for any DHCP server to give it an address.

You have to leave your equipment off for longer than the lease period for it to affect your assignment. Some ISPs have very short lease periods though.

Your address jump probably means that your ISP is reorganizing it's address pools for various reasons.

In addition to getting an I.P. address, the DHCP assignment process delivers other information to the computer, including the subnet name, DNS servers, and routing information. In some cases the subnet name is required to make sure that you reach the preferred (or only working) mail, news, and other local servers for your ISP.

-John
Personal Opinion Only