What does /32 mean?
A /32 matches exactly one IPv4 address. All 32 bits are fixed, so 203.0.113.10/32 means 203.0.113.10 and nothing else. The netmask is 255.255.255.255.
Worked example: 203.0.113.10/32. Type any block to compare.
203.0.113.10/32 is 1 address: 203.0.113.10 to 203.0.113.10. A /32 is a single host.
- Network
203.0.113.10- First usable
203.0.113.10- Last usable
203.0.113.10- Broadcast
none (/32)- Addresses
1- Usable hosts
1- Netmask
255.255.255.255- Wildcard (ACL) mask
0.0.0.0- Historic class
C- Range type
Documentation (TEST-NET-3) · not routed on the internet
Special-purpose range
Documentation (TEST-NET-3) 203.0.113.0/24 RFC 5737
Reserved for examples in documentation.
Split it into subnets
Is this IP in the range?
Range to CIDR blocks
What to know
/32 is how you write a single address wherever a CIDR block is expected: an allowlist entry, a security group rule (the AWS console's "My IP" option inserts your address as a /32), or a host route that sends traffic for one address a specific way.
Routers give their loopback interfaces /32 addresses so each router has one stable address for management and routing protocols.
Gotchas
- A home or mobile public IP changes from time to time. A /32 allowlist for "my IP" will stop working when your ISP assigns a new address.
- The IPv6 equivalent of a single-address /32 is /128. An IPv6 /32 is an enormous block, the size a regional registry typically allocates to an ISP.
Related explainers
- What does /31 mean?A /31 has 2 addresses and both are usable: RFC 3021 point-to-point links have no network or broadcast...
- What does /128 mean in IPv6?An IPv6 /128 is exactly one address, the IPv6 equivalent of an IPv4 /32. Used for loopbacks, host routes...
- What does 0.0.0.0/0 mean?0.0.0.0/0 matches every IPv4 address. In a routing table it is the default route; in a firewall or...
- IPv4 subnet cheat sheetEvery IPv4 prefix length from /0 to /32 with its netmask, total addresses and usable hosts. How to read...