100.64.0.0/10

100.64.0.0/10 is shared address space for carrier-grade NAT

Last updated 2 Nov 2026 from the IANA IPv4 Special-Purpose Address Registry

Short answer

100.64.0.0/10 is shared address space for carrier-grade NAT: your provider gives this to your router and shares a public address among many customers.

Block	100.64.0.0/10
First – last	100.64.0.0 – 100.127.255.255
Size	4,194,304 addresses
Name in the registry	Shared Address Space
Defined in	RFC 6598
Allocated	2012-04
Valid as source / destination	True / True
Forwardable	True
Globally reachable	False

What it means

RFC 6598 created 100.64.0.0/10 for internet providers that run carrier-grade NAT (CGNAT). Instead of giving each customer’s router a public IPv4 address, the provider gives it one from this range and translates traffic to a public address shared with other customers.

If your router’s WAN (internet) address starts with 100.64 to 100.127, you are behind CGNAT. Websites see the provider’s shared public address. Port forwarding from the internet to your home usually won’t work, and a block placed on that shared address affects everyone behind it.

What to do

Compare your router’s WAN address with your public address on the CGNAT check.
If you need incoming connections, ask your provider whether it offers a dedicated public IPv4 address, or use IPv6 if you have it.

Want the address websites actually see for you? Open the Truth Check.

Sources

IANA IPv4 Special-Purpose Address Registry (CC0) · checked 2 Nov 2026
RFC 6598