Why Your Home IP Address Changes

The Internet ran out of addresses in 2011. Everything since then has been improvisation.

If you've checked your IP address on two different days and noticed it changed, you've discovered something fundamental: your home doesn't have a permanent address on the Internet. It has a timeshare—a temporary assignment that works until it doesn't, then gets reassigned to whoever needs it next.

The Problem: Not Enough Addresses

The Internet runs on IPv4, a protocol designed in 1981 that provides about 4.3 billion unique addresses. That seemed infinite at the time. It isn't.

With billions of devices online, we've run out. Not metaphorically—literally. No new IPv4 addresses exist to assign. So ISPs improvise: they share addresses, rotate them, and layer them in ways that stretch limited supply across exponentially more users.

Your IP address isn't yours. It's on loan. Your ISP assigns it temporarily, then reassigns it when you disconnect or when they need it elsewhere. This is a dynamic IP address.

Your IP address might not even be unique. Increasingly, ISPs use Carrier-Grade NAT (CGNAT) to share one public address across hundreds of households. You appear to have an IP when you check, but so do dozens of strangers. You're timesharing.

External vs. Internal: Two Different Addresses

Your router assigns each device in your home a local address like 192.168.1.x—this is how your laptop talks to your phone. These internal addresses only work inside your house and stay stable unless you reconfigure your router.

Your external IP is different. It represents your entire household to the outside Internet. When you visit a website, it sees this address—not your individual device's internal one. This is the IP that changes.

The internal address is stable. The external one is borrowed.

What Triggers an IP Address Change

Your external IP doesn't shift randomly. Specific events cause reassignment:

Modem or Router Restart: When your modem disconnects—power outage, restart, brief network issue—it drops its IP address. When it reconnects, the ISP may assign a different one from the available pool.

Lease Expiration: Your ISP doesn't give you an IP address; it leases one for a set period, typically days to weeks. When that lease expires, your modem requests renewal. The ISP might return the same address or assign a new one, depending on availability.

ISP Network Maintenance: When your ISP upgrades equipment or rebalances network load, they may reassign addresses across their entire customer base without warning.

DHCP Pool Changes: If your ISP adjusts the size or range of their available addresses, existing leases may not renew with the same assignment.

How Often Does This Actually Happen

Frequency varies dramatically by ISP:

Every Connection: Some ISPs assign a new address every time your modem connects. Restart daily, get a daily change.

Weekly or Monthly: Many ISPs keep your IP stable for weeks or months as long as your connection stays active and leases renew successfully. Industry data shows about 16% of IPv4 addresses change location within a month, and 44% change within a year.

Rarely: Some ISPs provide "sticky" dynamic IPs that rarely change unless there's maintenance or a prolonged outage. While not technically static, they remain stable for months.

CGNAT Variability: Behind CGNAT, your apparent public IP might change more frequently and unpredictably, since you're sharing an address pool with many other users.

There's no universal rule. It depends entirely on your ISP's infrastructure and policies.

When CGNAT Makes You Invisible

Normally, your router uses NAT (Network Address Translation) to share one public IP among all your devices. CGNAT adds another layer: your ISP uses NAT to share one public IP among hundreds of customers.

You appear to have a public IP address when you check it. But that address isn't yours alone:

You cannot receive incoming connections. No one on the Internet can reach your devices directly. Hosting servers, running game servers, using certain peer-to-peer applications—all impossible.

You inherit other people's reputations. If someone sharing your IP violates a service's terms, you might get blocked or rate-limited. Services see you as the same user.

Some applications behave erratically. Any software that assumes one IP equals one user will misfire. Security measures designed for unique addresses create collateral damage.

You probably don't know you're behind it. CGNAT is invisible until you try to use features that require a unique public IP.

You can detect CGNAT by checking your router's WAN IP address.¹ If it falls in the range 100.64.0.0 to 100.127.255.255, you're behind carrier-grade NAT. That range is reserved specifically for this purpose.

When a Changing IP Actually Matters

For most browsing, streaming, and email, a changing IP is invisible. Nothing breaks. But certain uses require stability:

Hosting Servers: Running a web server, game server, or any service others connect to? A changing IP means they can't reliably find you. The address that worked yesterday won't work today.

Remote Access: Connecting to your home network remotely—security cameras, NAS devices, home computers—becomes difficult when your IP keeps shifting.

IP-Based Security: Some services use IP whitelisting, allowing access only from specific addresses. If your office VPN or banking application expects a consistent IP, frequent changes trigger security alerts or lockouts.

Port Forwarding with CGNAT: Behind CGNAT, port forwarding doesn't work at all. You don't have a unique public IP, so external devices can't reach specific ports on your network even with correct router configuration.

Solutions When You Need Stability

Static IP from Your ISP: Pay $5-$15/month for a permanent, dedicated address that never changes. Some ISPs only offer static IPs on business plans; some residential ISPs don't offer them at all.

Dynamic DNS (DDNS): A workaround that doesn't require paying for a static IP. DDNS gives you a permanent domain name (like yourname.ddns.net) that automatically updates to point to your current IP whenever it changes. Services like No-IP and DynDNS offer free or low-cost plans. Your router or a small client keeps the service updated, so you always reach your home network using the same domain name.

VPN with Static IP: Some VPN providers offer dedicated static IP addresses. This doesn't change your ISP-assigned IP, but gives you a consistent external identity when connecting through the VPN—useful for remote access scenarios.

IPv6 Adoption: If your ISP supports IPv6, you may get a unique address that remains more stable than IPv4. IPv6 has 340 undecillion addresses—enough for every device ever made to have trillions of unique addresses each. This eliminates the scarcity that created dynamic IPs and CGNAT. However, not all ISPs or services fully support IPv6 yet.

The Larger Pattern

Dynamic IP addresses and CGNAT aren't bugs. They're solutions to a fundamental architectural problem: we built a global communication system and ran out of addresses.

IPv6 will eventually fix this. But adoption is slow. ISPs must upgrade infrastructure. Websites must support dual-stack networking. Until then, we live in the improvisation: shared addresses, temporary assignments, invisible middlemen.

Your IP address changes because scarcity forces sharing, and sharing requires rotation. It's not permanent because permanence requires abundance we don't have.

You don't have an address on the Internet. You have a timeshare.

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