If you rely on any sort of service that requires you to know the IP address of your home internet connection, there’s a good chance you’ve noticed that the number (however frequently or infrequently) changes. Why is that?

图片由动态DNS服务提供商EasyDNS提供。

今天的问答环节是由SuperUser提供的，SuperUser是Stack Exchange的一个分支，是一个由社区驱动的问答网站分组。

问题

超级用户读者Agz很好奇为什么他的ISP不给他一个固定的IP地址：

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.

为什么呢？为什么不给每个顾客分配一个永久地址呢？

答案

SuperUser contributor Flimzy提供了对IP分配方法的一些见解：

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 connecti*** have become more common, the practical reas*** for not assigning a static IP have become much less noticeable, as now the majority of connecti*** 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 “c***umer” 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 c***umer-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.

既然你知道为什么你经常收到一个不同的IP地址，看看我们的文章如何轻松地访问您的家庭网络从任何地方与DDNS配置您的家庭网络使用免费的动态DNS服务，轻松找到回家的路，无论多少次您的ISP改变您的IP。

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