Two different situations
A home double NAT often appears when a personal router is placed behind a box that is already doing NAT. With the CGNAT, several subscribers share a public IPv4 at the operator level.
Compare addresses
Compare the router's WAN address with the publicly displayed one. A private WAN typically indicates upstream equipment. An address in 100.64.0.0/10 is a strong hint of CGNAT, but the full architecture must be considered.
Practical consequences
Gaming, incoming VPNs, cameras, or home servers may encounter inaccessible ports. Adding redirects on the last router is not enough if another translation is still present upstream.
Possible solutions
For home double NAT, use bridge mode, an access point, or consistent redirection on both devices if possible. For CGNAT, request a public or full stack IPv4 from the operator, use IPv6 or a suitable outbound tunnel.
Frequently asked questions
Does 100.64.x.x still mean CGNAT?
This range is reserved for the shared space of the operators and is a strong indication, to be confirmed with your supplier.
Does the DMZ of the box remove double NAT?
It sometimes simplifies redirects, but the box usually continues to perform a translation. Bridge mode is different.
Reference sources
To be explored next
Published and verified by the VoirMonIP.com team on July 15, 2026.