SPs change your IP address


Is there any specific reason an ISP will need to change your IP address? What is the purpose of a dynamic IP versus a static IP? For me it seems to happen every 6 months, while for someone I know, it does once a week.

Best Answer

When ISPs were first starting, everyone connected to the Internet over a modem. And most people used the Internet for a few minutes to a few hours per week. Assigning a static IP to every subscriber would have been very expensive, for something that most people used just a few minutes a week.

As broadband connections have become more common, the practical reasons for not assigning a static IP have become much less noticeable, as now the majority of connections are "always-on"--even when nobody is (actively) using the Internet.

So there's a bit of a historical reason not to use static IPs--customers are already accustomed to using dynamic IPs.

When modern ISPs enforce dynamic IPs these days, it may be in part to distinguish between "consumer" and "professional" services--by reserving static IPs for customers who pay more, it gives customers who need that feature an incentive to upgrade their service level.

It can also serve as a deterrent for people abusing their consumer-grade service. Many ISPs, for instance, explicitly prohibit running "servers" on a home Internet connection. If every home user had a static IP, they'd be more inclined to abuse such terms of service.

It's also less of a management problem to assign customers dynamic IPs. If you move across town (but within the same ISP's service area), there's no need to re-assign how your static IP is routed; you'll just get a dynamic IP that exists in the new neighborhood.