If the WAN address on the router and the public IP the website points to are different, there may be some address translation. This comparison is an important clue for port forwarding problems.

Basic approach

100.64.0.0/10 is reserved for shared addressing use by service providers. This range is not the same category as RFC 1918 private addresses. The presence of addresses from this block on the WAN side of the router suggests the use of CGN; Your provider verifies the exact terms of service.

Application steps

  1. Take note of the router's WAN IPv4 address and the IPv4 address visible over the web at the same time.
  2. If you are using a VPN or proxy, determine if the comparison is affected by them.
  3. When discussing incoming connection needs with your ISP, ask separately for general IPv4, CGN and IPv6 options.

Practical example

If the WAN address is 100.72.10.8 and a different address appears outside, turning on the port rule on the local modem may not provide end-to-end access on its own. The translation of the provider at the upper layer is also part of the connection path.

Interpret the result correctly

Address difference alone is not evidence of CGN; Dual routers, corporate egress, or VPN can also create the same symptom. Be careful not to compare the IPv4 address with the IPv6 address when examining.

Source and follow-up reading

Protocol or command details: RFC 6598. The steps and example scenario are IPScans editorial narrative.