[ivanjermakov]

I subtly remember that 10.x.y address space is widely used by CGNATs.

[greyface-]

CGNATs should be using 100.64/10 instead of 10/8 to avoid this problem, but I don't doubt that there are significant deployments on 10/8 anyway.

[zinekeller]

The IETF really dragged their heels on CGNAT because they thought that IPv6 is easy™ (of course not, it's intentionally designed not to be "almost the same but wider" but include unworkable stuff like Mobile IPv6[1] which is just a fancy VPN) until they were forced to allocate 100.64.0.0/10 because some ISPs are not just using 10.0.0.0/8 but also US-DoD addresses (especially 11.0.0.0/8, because it's basically 10.0.0.0/7) as "private" addresses.

[1] Not IPv6 on mobile devices but a fully-owned IPv6 range that is supposed to be the address for a device regardless of where it is, see RFC 3775

[pcarroll]

I wanted to use 11.0.0.0 and call the company "Eleven," but by that time the DOD had given up the block for general use... GCNAT is perfect.

[rtkwe]

Are those usually visible to clients sitting behind routers though? I'm not super familiar but the things I'm seeing make it seem like that should only be visible IPs on the internal network of carriers which is not a place I am ever connecting from.