127.0.0.0/8
Loopback RFC 5735The 127.0.0.0/8 range is reserved for loopback addresses. Any packet sent to an address in this range stays on the local host and is never transmitted on a network. 127.0.0.1 is the canonical "localhost" address.
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 127.255.255.255 are delivered to every device in the subnet. Also reserved — not assignable.
Usable hosts — the 16,777,214 addresses between those two that you can assign to servers, VMs, or interfaces.
Subnet mask — 255.0.0.0 is the dotted-decimal equivalent of /8. Older tools and Cisco configs use this format instead of CIDR slash notation.
Full Details
| CIDR Notation | 127.0.0.0/8 |
| Network Address | 127.0.0.0 |
| Broadcast Address | 127.255.255.255 |
| Subnet Mask | 255.0.0.0 |
| Wildcard Mask | 0.255.255.255 |
| Prefix Length | /8 |
| IP Address Class | Class A |
| Total IP Addresses | 16,777,216 |
| Usable Host Addresses | 16,777,214 |
| First Usable IP | 127.0.0.1 |
| Last Usable IP | 127.255.255.254 |
| Network (Hex) | 0x7F000000 |
| Broadcast (Hex) | 0x7FFFFFFF |
| Governing RFC | RFC 5735 |
| Address Type | Loopback |
Binary Representation
The first 8 bits (1s in the mask) identify the network. The remaining 24 bits identify hosts within the network.
Subnet Breakdown — splitting into /9
This /8 block can be divided into 2 /9 subnets.
| CIDR | Network | Broadcast | First Usable | Last Usable | Hosts |
|---|---|---|---|---|---|
| 127.0.0.0/9 | 127.0.0.0 | 127.127.255.255 | 127.0.0.1 | 127.127.255.254 | 8,388,606 |
| 127.128.0.0/9 | 127.128.0.0 | 127.255.255.255 | 127.128.0.1 | 127.255.255.254 | 8,388,606 |
Common Use Cases
- → localhost — connecting to services on the same machine
- → Software testing without network access
- → Inter-process communication on a single host