Dynamic vs Static I/P with Comcast?

Yep, not likely to change unless your cable segment gets congested and they decide to split your segment. You address might change if you wind up on the new split side.

Why would you want to change it. I like the almost static address so I can use it to kill file morons in Usenet posts.

Yep, looking at my dhcp lease from comcast here in Dallas. Obtained Fri Sep 22 22:41:58 CDT 2006 Renewal 2006/9/24 19:29:26; Rebind 2006/9/26 15:41:56; Expires 2006/9/27 03:41:56; I would have to leave it off past the expiration date to have a ghost of a chance of loosing it. Then several other people would have to leave theirs off for the same period or a bunch of new customers would have to get added to my segment to force the dhcp server to re-use my expired address. Not much chance of that.

Buy a new interface card and connect it to the cablem modem.

"Bill Crocker" wrote in news:c_qdnenn1KYx3IjYnZ2dnUVZ snipped-for-privacy@comcast.com:

If you have a NAT router, change the internet(WAN) MAC address of it. That always changed the IP I was assigned by RR. If I changed it back a week later, I got the previous one that I had for 5+ years. I liked the "static" IP. However, recently RR reconfigured this area and I now have a new IP in a different range, and so far it's holding static. Comcast may do the same.?? You will probably have to power down the cable modem for a couple of minutes for the new IP to be acquired.

You're describing the very nature of any fixed network, whether it uses static IP's or DHCP. IP addresses will not change unless there is a need for them to change.

The difference is that when using DHCP, the changes that need to occur happen automatically. With static IP's, when changes have to be made, someone has to manually make them, and make them during the right time window. That's not practical when so many pieces of equipment are located inside thousands of private residences.

Even with DHCP, your IP address does not change unless it has to. The DHCP server will continue to give out the same IP addresses to the same equipment as long as it's possible. Disconnect and reconnect as many times as you want, but you'll continue to get the same IP address. It won't change until there is a network reconfiguration that requires a renumbering.

This differs from dial-up. With dial-up, if you disconnect, and reconnect you are, depending on how busy things are, likely to get a different IP. That's because the fixed part of the network ends at the modem rack. At the PoP there will be a rack with, let's say, 64 modems on it. The first call to the access phone number goes to the first modem in the rack, the second call to the second modem, etc. And when someone disconnects, the next person to call in fills that empty space. So at a busy PoP, each time you dial-in, you'll get a different modem. In a network like this, they only have enough IP addresses to give each modem an IP address, not each possible user who might connect to the modems. So the IP address you'll get will depend on which modem you connect to.

With a cable internet system, theoretically everyone is always connected, so there must be enough IP addresses for each user. All IP addresses will always be in use. There's absolutely no reason to vary from normal networking practices of the DHCP server always giving the same IP address to the same equipment. That's the way DHCP normally works, and there's no need to confuse things by randomly juggling IP addresses around.

Essentially, whether you configure things by DHCP or manually, IP addresses should not change unless they need to. Using DHCP just means someone doesn't have to make a manual change to each piece of equipment. DHCP allows any change to be transparent to the end user. That's it. It does not mean your IP address will change. It only means that if it has to change, you won't be required to make the change manually on your end at a prescribed time.

As other posted, the IP address is roughly based on the MAC address your computer or router passes on to the modem. Comcast tends to tie an IP address to a particular modem MAC/computer MAC address for quite awhile. It typically changes only if you change one of the MAC address, stay offline for a very long time (I've been off for a few days and still had the same address), or Comcast makes some structural changes in their network.

The last time mine changed was a few months ago, when I went through several address over a few days. This was just before they started there 'PowerBoost' feature.

In very simple terms.

Dynamic vs. Static is an arrangement you have with the people upstream from you.

If it's static it should not change without people getting involved and coordinating it. I.E. the upstream has committed you'll get the same IP until they change the deal with you.

If it's dynamic the upstream can change it anytime they want within the rules of PPPoE, PPPoA, DHCP, or however your connection is made.

Now as a practical mater a static can change and a dynamic not change give the above. It's up to the upstream.

For a variety of reasons, cable companies seem to not change dynamic IPs very often, and many ILEC DSL providers seem to change them on a whim.

And, if you stay on the same CMTS, it is unlikely to change either, due to interface bundling. Normally, a CMTS (or any router, for that matter), segments subnets via hard interfaces. However, this tends to be inefficient and eats up a lot of IP address space or requires a lot of administration (this happened all the time in the bad old days with @home. They ALWAYS underestimated subnet requirements and we ran out of addresses every few weeks). Cisco introdced interface bundling to help combat this problem, basically turning the CMTS into a switch instead of a router. Works like a champ, makes everyone happy. Of course if you are in a major metro area, you will likely see new devices added and nodes moved to the new device, not a reshuffle.