Why ISPs Assign Dynamic vs Static IP Addresses


If you have ever sought to find your public IP address, you may have noticed that it changes every so often. This is called a dynamic IP address because it can change at even given moment. Most ISPs will assign dynamic IP addresses to their consumer clients for a variety of reasons. If you wanted a static IP address, you normally would have to upgrade to a business account, if it’s available in your area.

The assignment of dynamic IP addresses to consumers actually has a bit of history behind it and the original reason for using dynamic IP addresses is not exactly the same as it is now. So what are the advantages and disadvantages of having a dynamic vs static IP address assigned to your Internet connection? In this article, I’ll explain the reasons behind the current day usage of dynamic IP addresses by ISPs.

Advantages of Static & Dynamic IP Addresses

Firstly, let’s go through the actual advantages and disadvantages of static vs dynamic. The main reason why most people get dynamic IP addresses and it doesn’t really matter to them is because they don’t need have clients making inbound connections to their computers. Static IP addresses are needed by users who are hosting services from their servers or computers. Here are a couple of examples:

– FTP Server

– Web Server

– Gaming Server (XBox, PlayStation)

– Virtual Private Network (VPN)

– Email Server


– Remote Desktop

For most people, this is not something they plan to setup and therefore a static IP is not needed. A lot of ISPs also actively discourage and prevent users from hosting servers from home. With a static IP address, it’s a lot easier to setup a mail server and start spamming the world then if you have a dynamic IP address assigned. It’s also a lot easier to setup P2P servers where users can share large collections of copyrighted movies, music, etc. This ends up causing more problems and hurting the people who are not abusing the network.


Remember the days when you had to wait a whole minute while your computer connected to the Internet? After you were done, you also had to disconnect so that you didn’t use up all of your bandwidth for the month. In those times, you probably only connected to the Internet for a few minutes to a few hours a day.


To assign a static IP address to a user who only connects for a short period of time would have been cost prohibitive. Instead, when one user disconnected and another connected, it was a lot easier and cheaper to just assign that IP address to the newly connected client. So in some sense for historical reasons, ISPs assign dynamic IP addresses rather than static. However, that’s no longer the main reason.

Maintenance/Configuration & IPv4

When a user is assigned a static IP address, it means they will have that one IP address all the time. This requires extra work on the part of the ISP because it requires extra configuration to setup a static IP address. Not only that, but if you decide to move to another area where the ISP is the same, you’ll probably want the same IP address and that also requires extra configuration.

The other problem occurs when a piece of hardware has to be replaced or upgraded. If the router is replaced, then the static IP has to be manually configured again on the new router. With a dynamic IP address, the router can be replaced and will work just fine without any additional configuration of the IP address.

Also, if everyone was to get a static IP address, it would be highly inefficient. For example, if someone turns off their machine at home and is not using their Internet connection, then that IP address is still locked with that user. ISPs only have certain blocks of IP addresses they can work with, so the more IP addresses they can reuse, the better.


Currently in the IPv4 system, there is a shortage of IP addresses. This is also the reason why your local network uses private IP addresses that start with numbers like 10.0.x.x or 192.168.x.x. If you were to try to assign a static IP address to every Internet-connected device in the world, it would be impossible because there aren’t enough actual IP addresses.

That’s where IPv6 is supposed to come in and alleviate the problem. IPv4 addresses are 32 bits in length and therefore can only support about 4.29 billion addresses. IPv6 uses 64 bits and therefore can support 340,282,366,920,938,000,000,000,000,000,000,000,000 addresses! That’s such a huge number, I don’t even know what to call it. You can read more about IPv4 vs IPv6 on Mashable.

ISP Pricing Structures

Another reason why ISPs don’t give everyone a static IP address is that they can make more money by charging for a static IP address. As I had mentioned above, you can do a lot more stuff with a static IP address. Of course, you could always setup something called dynamic DNS, which keeps track of a changing dynamic IP address and lets you connect using a DNS name rather than the IP address, but it’s definitely more complicated and not nearly as seamless as having a static IP address.

Some ISPs like mine, AT&T, charge a monthly fee for giving you a semi-static IP address. I say semi-static, because it’s just a reservation in the DHCP server, which means it won’t change unless there is an extreme circumstance. I believe it’s $15 a month off 5 and it goes up from there. Other ISPs charge more or less, just depends. Some don’t even offer it in residential areas.


Last, but not least, dynamic IP addresses provide more security than static IP addresses. When a static IP address is assigned, it makes it a lot easier to perform long repeated attacks on that IP address. For those with dynamic IP addresses, there is a less security risk because the IP address changes and therefore you are less prone to repeated attacks.

Also, static IP addresses are easier to track by companies or hackers. Most websites already try to track your browsing habits so that they can show you more personalized ads and with a static IP address, it’s even easier to do this.

On the client side, a user can make the network less secure or less stable by using a static IP address for nefarious purposes. Even though most ISPs cap the amount of bandwidth that a single user can consume, someone with a static IP could still eat up a lot of bandwidth indirectly. For example, if someone is hosting a website from their home using a static IP address and hackers decide to level a DDOS attack on the site, the ISP will get flooded with traffic, which could cause slowness or outages for other customers.

Hopefully, this article gives you a sense of why ISPs assign dynamic IP addresses to users and some of the advantages and disadvantages that this brings about. If you have any questions, feel free to leave a comment. Enjoy!

· · ·

Leave a Comment

This site uses Akismet to reduce spam. Learn how your comment data is processed.