What is an IP address, and why does it matter?

Every device that talks on a network needs a unique number so other devices can send things to it. That number is the IP address. The word "address" is doing the work — it is literally where to deliver packets. The internet is a packet-routing system; without an address, packets have nowhere to go.

Your phone has one. Your laptop has one. Your TV, NAS, smart bulb, and printer each have one. They are numbers between 0 and 255 in four blocks (192.168.1.42) for the old IPv4 format, or eight blocks of letters and numbers (2606:4700:4700::1111) for IPv6.

Inside your house, every device gets a private IP from the router. These addresses are reserved globally and are guaranteed never to be used on the public internet. The most common range is 192.168.1.x or 192.168.0.x, which gives a household 254 usable addresses on a single network — far more than most homes use.

When one of those devices asks for a website, the router translates the request to the single public IP your ISP gave the house, sends it out, and translates the reply back. The public IP is what shows up at whatismyip.com. Your private IP shows up only on the router's admin page.

The router explainer covers why the router is doing this translation in the first place.

The router runs a small service called DHCP — Dynamic Host Configuration Protocol — that hands out private IPs automatically. Each address comes with a lease time, usually 24 hours on a home router. When the lease expires, the device renews it and almost always gets the same address. If your phone has been off the Wi-Fi for a few days, the lease expires and it may get a different address next time.

In 2026 the bigger reason your phone's IP changes is **Private Wi-Fi Address** (iOS) or **Randomized MAC** (Android, Windows 11) — both default-on. The phone rotates the identifier it uses to talk to the router, the router sees a new device, and hands out a new IP. This can fill up the DHCP pool on small routers and cause IP conflicts.

When you want a device to always have the same IP — your NAS, printer, security camera, Home Assistant box — set a **DHCP reservation** in the router. The router keeps handing out the same address to that specific device.

IPv4 only has about 4.3 billion addresses globally, and the world ran out of new ones over a decade ago. IPv6 is the long-term fix — more addresses than there are grains of sand on Earth. As of March 2026, over half of all Google traffic globally goes over IPv6 (the US is around 50% too). But most home networks still default to IPv4 internally because that is what every device and app has supported for decades.

The short-term workaround ISPs use is **CGNAT** — they put hundreds or thousands of customers behind one shared public IPv4 address. You still have a public IP at home, but it is not really yours; you are sharing it. This is invisible for normal browsing, but it breaks anything that needs the outside world to reach in: Plex Remote Access, hosting a server, port forwarding, some VPN setups.

T-Mobile Home Internet, Starlink residential, Verizon 5G Home, mobile-hotspot tethering, and increasingly Spectrum and AT&T put residential customers behind CGNAT. If Plex Remote Access stopped working in 2025-2026 and nothing changed at your house, CGNAT is the most likely cause — the CGNAT diagnostic page walks through confirming it.

People conflate several different addresses under the word "IP," and they change for different reasons. Your **public IP** may rotate every few days when your ISP's lease expires. Your **private IP** changes when your phone reconnects with a randomized address. Your **VPN IP** is whichever address the VPN provider's exit node has at the moment.

None of these are "your" IP in any permanent sense — they are all temporary labels. If you want true persistence for a device inside your house, set a DHCP reservation. If you need a permanent public IP for hosting something, ask your ISP for a static IP — often $5-15/month on business-tier plans, rarely on consumer plans.