The best-known /10 is 100.64.0.0/10, the “shared address space” from RFC 6598. ISPs use it for carrier-grade NAT: if your router’s WAN address starts with 100.64 to 100.127, your ISP puts you behind CGNAT and you share a public IP with other customers. That breaks inbound port forwarding, which is why a port checker shows your ports as closed. Tailscale also uses this range for device addresses.
Facts
- Prefix
- /10
- Subnet mask
- 255.192.0.0
- Wildcard mask
- 0.63.255.255
- Binary mask
- 11111111.11000000.00000000.00000000
- Total addresses
- 4,194,304
- Usable hosts
- 4,194,302
- Example range
- 10.0.0.0/10: 10.0.0.0 – 10.63.255.255
- Typical use
- Carrier-grade NAT: 100.64.0.0/10 is the shared address space ISPs use for CGNAT.
Try it
Try: , ,
- CIDR block
- 10.0.0.0/10
- IP range
- 10.0.0.0 – 10.63.255.255
- Addresses
- 4,194,304
- Usable hosts
- 4,194,302
- Subnet mask
- 255.192.0.0
- Wildcard mask
- 0.63.255.255
Frequently asked questions
How many hosts are in a /10?
A /10 has 4,194,304 addresses. Subtracting the network and broadcast addresses leaves 4,194,302 usable hosts.
What is the subnet mask for /10?
/10 is 255.192.0.0 (wildcard mask 0.63.255.255). In binary that’s 10 ones followed by 22 zeros.