100.64.0.0/10
Public100.64.0.0/10 is reserved for Carrier-Grade NAT (CGNAT) as defined by RFC 6598. ISPs use this range to perform NAT between their customers and the public internet, helping extend the life of IPv4.
Network address — the base address of the block (100.64.0.0). All devices in this subnet share this prefix. Cannot be assigned to a host.
Broadcast address — packets sent to 100.127.255.255 are delivered to every device in the subnet. Also reserved — not assignable.
Usable hosts — the 4,194,302 addresses between those two that you can assign to servers, VMs, or interfaces.
Subnet mask — 255.192.0.0 is the dotted-decimal equivalent of /10. Older tools and Cisco configs use this format instead of CIDR slash notation.
Full Details
| CIDR Notation | 100.64.0.0/10 |
| Network Address | 100.64.0.0 |
| Broadcast Address | 100.127.255.255 |
| Subnet Mask | 255.192.0.0 |
| Wildcard Mask | 0.63.255.255 |
| Prefix Length | /10 |
| IP Address Class | Class A |
| Total IP Addresses | 4,194,304 |
| Usable Host Addresses | 4,194,302 |
| First Usable IP | 100.64.0.1 |
| Last Usable IP | 100.127.255.254 |
| Network (Hex) | 0x64400000 |
| Broadcast (Hex) | 0x647FFFFF |
| Address Type | Public / Globally Routable |
Binary Representation
The first 10 bits (1s in the mask) identify the network. The remaining 22 bits identify hosts within the network.
Subnet Breakdown — splitting into /11
This /10 block can be divided into 2 /11 subnets.
| CIDR | Network | Broadcast | First Usable | Last Usable | Hosts |
|---|---|---|---|---|---|
| 100.64.0.0/11 | 100.64.0.0 | 100.95.255.255 | 100.64.0.1 | 100.95.255.254 | 2,097,150 |
| 100.96.0.0/11 | 100.96.0.0 | 100.127.255.255 | 100.96.0.1 | 100.127.255.254 | 2,097,150 |
Common Use Cases
- → ISP Carrier-Grade NAT infrastructure
- → Tailscale VPN overlay network (100.x.x.x)
- → Large-scale NAT deployments