ipSharing at the provider level
CGNAT allows an ISP to share a public IPv4 address among multiple subscribers. Another translation layer may sit in front of your home router. Ordinary browsing can work while connections initiated from outside encounter problems.
Which addresses to compare
Compare your router’s WAN address with the public IPv4 shown by a website. The 100.64.0.0/10 shared address space can be used in CGNAT deployments. A private or mismatched WAN address may indicate another NAT layer, but a single observation does not prove the full topology. Confirm with your ISP.
Remote-access options
Opening a port only on your router does not resolve the ISP’s NAT layer. Depending on your needs, consider a public IPv4 service, suitable IPv6 connectivity, or a secure outbound tunnel. IPv6 still requires firewall policy; obtaining a public address does not automatically provide safe access.
Comparing WAN and external addresses
If the router WAN page shows 100.64.10.20 while a lookup shows another IPv4, investigate provider-level translation. Send the addresses and test time to support. Do not confuse the WAN value with a LAN address. Before repeatedly changing port-forwarding rules, ask whether a public IPv4 or alternative access service is available.
Further reading
Shared address space — RFC 6598 ↗Put it into practice
Inspect one public IP, or compare a list of addresses with the bulk lookup tool. Location results are approximate.
Single lookup ↗ Bulk lookup ↗