Question 1

What is CGNAT, and why does it break things?

Accepted Answer

**Carrier-grade NAT** is a technique ISPs use to share a single public IP address between many customers — a response to IPv4 address exhaustion, and a cause of a specific and confusing set of problems.

**The underlying problem.** IPv4 has about 4.3 billion addresses, and they ran out. Regional registries have been allocating from scarce reserves for years. IPv6 solves it permanently but adoption has been gradual, so ISPs needed an interim measure.

**What CGNAT does.** Instead of giving each customer a public address, the ISP assigns a **private** address from its own range and performs a second layer of address translation in its network. Dozens or hundreds of customers appear to the outside world as **one** public IP address, distinguished by port numbers.

This is the same principle your home router already uses for devices in your house — CGNAT simply does it again, one level up.

**What it breaks:**

**Inbound connections.** Nothing outside can initiate a connection to you, because your address is not routable. This breaks **port forwarding** entirely, and with it self-hosted servers, security camera access from outside, remote desktop, and home automation reachable from away.

**Peer-to-peer and gaming.** Some multiplayer titles and voice systems struggle, reporting a **strict NAT type**. Games generally work but hosting or direct connection may not.

**Dynamic DNS becomes useless**, since the address is not yours.

**Shared reputation.** If another customer behind the same address is abusive, the address can be rate-limited or blocked — which is why you may suddenly face repeated CAPTCHAs or a block on a site you have never misused.

**Geolocation becomes less accurate.**

**How to tell if you are behind it.** Compare the WAN address shown in your router with the address a "what is my IP" site reports. **If they differ, you are behind CGNAT.** A WAN address in ranges such as 100.64.0.0/10 is a strong indicator.

**What to do:** many ISPs will move you off CGNAT or provide a static IP on request, sometimes for a fee. **IPv6**, where offered, gives genuinely routable addresses and sidesteps the problem.

Question 2

What is NAT, and why does every home network use it?

Accepted Answer

Network Address Translation lets many devices share one public IP address, by rewriting addresses and ports as traffic passes through the router. Why it exists. IPv4 provides around 4.3 billion

Question 3

How accurate is IP geolocation?

Accepted Answer

Reliable at country level, decent at city level in dense areas, and frequently wrong at any finer resolution — because an IP address contains no location information at all. Everything is inference

Question 4

What is BGP, and why does it sometimes break the internet?

Accepted Answer

Border Gateway Protocol is how independent networks tell each other which addresses they can reach. It is the routing system the entire internet depends on — and it works largely on trust, which is

Question 5

Why did the internet run out of IPv4 addresses, and how are they traded now?

Accepted Answer

Because the address space was fixed at 32 bits — about 4.3 billion addresses — in 1981, when the internet was a research network and nobody expected every household to hold dozens of connected

Question 6

What is an IP address and what is the difference between public and private?

Accepted Answer

An IP address identifies a device on a network so traffic can be routed to it. The important distinction for everyday troubleshooting is between the address your device holds on your local network

Question 7

What is anycast, and how can one IP address be in many places?

Accepted Answer

Anycast announces the same IP address from multiple locations, and the routing system naturally delivers each user's traffic to whichever location is closest in network terms. It is one of the more

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