127.0.0.0/9
Loopback RFC 5735Class A — /9 prefix — 8,388,606 usable hosts
Network address — the base address of the block (127.0.0.0). All devices in this subnet share this prefix. Cannot be assigned to a host.
Broadcast address — packets sent to 127.127.255.255 are delivered to every device in the subnet. Also reserved — not assignable.
Usable hosts — the 8,388,606 addresses between those two that you can assign to servers, VMs, or interfaces.
Subnet mask — 255.128.0.0 is the dotted-decimal equivalent of /9. Older tools and Cisco configs use this format instead of CIDR slash notation.
Full Details
| CIDR Notation | 127.0.0.0/9 |
| Network Address | 127.0.0.0 |
| Broadcast Address | 127.127.255.255 |
| Subnet Mask | 255.128.0.0 |
| Wildcard Mask | 0.127.255.255 |
| Prefix Length | /9 |
| IP Address Class | Class A |
| Total IP Addresses | 8,388,608 |
| Usable Host Addresses | 8,388,606 |
| First Usable IP | 127.0.0.1 |
| Last Usable IP | 127.127.255.254 |
| Network (Hex) | 0x7F000000 |
| Broadcast (Hex) | 0x7F7FFFFF |
| Governing RFC | RFC 5735 |
| Address Type | Loopback |
Binary Representation
The first 9 bits (1s in the mask) identify the network. The remaining 23 bits identify hosts within the network.
Subnet Breakdown — splitting into /10
This /9 block can be divided into 2 /10 subnets.
| CIDR | Network | Broadcast | First Usable | Last Usable | Hosts |
|---|---|---|---|---|---|
| 127.0.0.0/10 | 127.0.0.0 | 127.63.255.255 | 127.0.0.1 | 127.63.255.254 | 4,194,302 |
| 127.64.0.0/10 | 127.64.0.0 | 127.127.255.255 | 127.64.0.1 | 127.127.255.254 | 4,194,302 |