/32 Subnet Mask Reference (255.255.255.255)
Single host route, loopback interface, or exact firewall /32 allowlist rule.
| CIDR Prefix | /32 |
|---|---|
| Subnet Mask | 255.255.255.255 |
| Wildcard Mask (Cisco / ACL) | 0.0.0.0 |
| Total IPv4 Addresses | 1 |
| Usable Host IPs | 1 |
| Binary Subnet Mask | 11111111.11111111.11111111.11111111 |
| Example Block (10.0.0.0/32) | 10.0.0.0 – 10.0.0.0 |
| Example Usable Hosts | 10.0.0.0 – 10.0.0.0 |
Need to compute custom IP ranges? Try the Interactive Subnet Calculator or VLSM Splitter.
Understanding the IPv4 /32 CIDR Block
An IPv4 /32 prefix allocates 32 network bits and 0 host bits out of a 32-bit IPv4 address, yielding an address block of 2^0 = 1 total IPv4 addresses. Expressed in dotted-decimal notation, the subnet mask is 255.255.255.255, and its bitwise inverse—used in Cisco IOS access control lists (ACLs) and OSPF area statements—is wildcard mask 0.0.0.0.
A /32 prefix contains zero host bits and pinpoints a single exact IPv4 host. Network engineers use /32 routes for router loopback interfaces (BGP router-IDs and OSPF endpoints), WireGuard peer host routes, and single-IP firewall allowlists.