100.64.0.0/10 (Carrier-Grade NAT (also Tailscale))
Not routableRFC 6598
100.64.0.0/10 at a glance
| CIDR block | 100.64.0.0/10 |
|---|---|
| First address | 100.64.0.0 |
| Last address | 100.127.255.255 |
| Total addresses | 4,194,304 |
| Subnet mask | 255.192.0.0 |
| Prefix length | /10 |
| Type | Not routable |
| Publicly routable | No |
| Defined in | RFC 6598 |
Open in CIDR calculator/10 subnet details
What is 100.64.0.0/10 used for?
100.64.0.0/10 is the shared address space reserved by RFC 6598 for carrier-grade NAT, the layer of NAT that ISPs run between customers and the internet. It is not private in the RFC 1918 sense, but it is not publicly routable either. Overlay VPNs such as Tailscale also assign device addresses from it.
Common subnets of 100.64.0.0/10
Overlaps and conflicts
Tailscale uses this range for device addresses; if your ISP also uses CGNAT, some 100.x routes can conflict.
FAQ
Is 100.64.0.0/10 a public IP?
No. If your router's WAN address is in 100.64.0.0 – 100.127.255.255, your ISP uses carrier-grade NAT and you do not have a public IPv4 address.
Why does Tailscale use 100.64.0.0/10?
Tailscale assigns device addresses from 100.64.0.0/10 because that range is rarely used on home and office LANs, so it is unlikely to collide with existing private networks. It can conflict if your ISP also uses carrier-grade NAT.