Every internet connection gets a public IP address. On some, it never changes; on most, it changes from time to time. For browsing, streaming and gaming, that makes no difference. For reaching cameras, a server or your office computer from outside, it makes all the difference.
The difference
- Dynamic IP: the ISP assigns an address from its pool on each connection. When the modem restarts, the power goes out or a certain amount of time passes, the address may change. This is the default for residential connections.
- Static IP (or fixed IP): the address is reserved for you and does not change. It is usually sold as an add-on or included in business plans.
How to tell which one you have
- Open My IP and write down the address.
- Restart your ISP's modem or router and wait for the connection to come back.
- Open My IP again. If the address changed, your IP is dynamic.
If it did not change, it may still be dynamic: many ISPs keep the same address for days or weeks. The definitive answer is in your contract or with customer support. If you never paid for a static IP, yours is almost certainly dynamic.
What about CGNAT?
There is a third situation that is increasingly common: CGNAT, where the ISP shares a single public IP among several customers. In that case, the IP shown on My IP is not yours alone, and incoming connections from outside never reach your home, not even with port forwarding.
Signs of CGNAT: the internet (WAN) IP shown in your router's panel starts with 100.64 to 100.127, or it differs from the IP shown on My IP. The fix is to ask your ISP for a public IP, which can be dynamic or static.
When a static IP is worth it
- A web, game or file server at home or in the office.
- Access to cameras, recorders (DVR/NVR) or home automation without relying on a cloud app.
- Systems that allow access by IP, such as databases, hosting panels or a company VPN.
- Your own mail server, which needs a static IP with reverse DNS set up.
For regular home use, a static IP is unnecessary, and it also exposes the same address all the time.
Free alternative: dynamic DNS
If your IP is dynamic but public (no CGNAT), a dynamic DNS (DDNS) service solves most cases. You create a name, such as myhome.ddns.net, and your router or a small program notifies the service whenever the IP changes. That way you connect by name, without memorizing the number. Many routers already include the option in their settings, with providers like No-IP and DynDNS, and several manufacturers offer their own free service.
Summary
- You restarted the modem and the IP changed: dynamic.
- The router's IP starts with 100.64 to 100.127: CGNAT. Ask your ISP for a public IP.
- You need access from outside and the IP changes: use dynamic DNS or get a static IP.
- You opened the ports and nothing works: see the guide how to check if a port is open.