Start with the right three addresses
Your device has an address on its local network. Your router has a separate WAN or Internet address. myip.dk reports the source address that reaches our public service. With a typical home IPv4 connection, the router translates traffic from several local devices onto one public address.
The private IPv4 ranges are 10.0.0.0–10.255.255.255, 172.16.0.0–172.31.255.255, and 192.168.0.0–192.168.255.255. They are reused on many networks. An address such as 192.168.1.20 identifies a device within your network, not a globally unique Internet destination.
Worked example: finding a second layer of NAT
Suppose your laptop shows 192.168.1.20, your router’s WAN page shows 100.72.8.9, and your public IPv4 is different. The laptop address is ordinary private space. The WAN address falls inside 100.64.0.0/10, the shared range reserved for provider networks. Together, those observations suggest carrier-grade NAT (CGNAT). Your ISP can confirm it.
If the WAN address is instead 192.168.0.2, look for another router or ISP gateway upstream. That may be double NAT inside the premises. A different public address alone does not establish CGNAT: a VPN, proxy, or multi-WAN connection can also explain it.
Make a useful comparison
Use addresses collected at the same time and on the same connection.
- Record the IPv4 shown here. If appropriate for your network, disconnect a VPN or browser proxy before comparing.
- Open the router’s administration page and find WAN or Internet IPv4. Do not compare its LAN gateway address.
- Check whether the WAN address belongs to a private range or 100.64.0.0–100.127.255.255.
- If you need incoming connections, ask the ISP whether the service includes a public IPv4 or an IPv6 prefix, and whether inbound traffic is filtered.
What the result cannot prove
Matching public and WAN IPv4 addresses does not prove that incoming ports are reachable. Router rules, device firewalls, and ISP filtering still matter. A website cannot inspect your router settings or reliably discover your LAN address from an ordinary HTTP request.
A public IPv6 address can coexist with CGNAT for IPv4. Diagnose the two address families separately; IPv6 normally uses firewall rules rather than an IPv4 port-forwarding rule.