What a /32 subnet is: a single host
A /32 is one address. It is how you name a specific host in a route, a firewall rule or an allowlist, and it is the most specific IPv4 prefix that exists.
At a glance
- Subnet mask
- 255.255.255.255
- Wildcard mask
- 0.0.0.0
- Total addresses
- 1
- Usable hosts
- 1 (a single host, not a subnet)
- Block size in the last octet
- 1
- Host bits
- 0 of 32
In detail
The mask is 255.255.255.255 and the wildcard mask is 0.0.0.0, so every bit must match. Longest-prefix matching means a /32 route always wins over any broader route to the same address.
Loopback interfaces on routers, host routes, allowlist entries, and the address form every firewall rule reduces to when you write a single address without a prefix.
When an allowlist entry is not matching, check whether the tool defaulted the missing prefix to /32 or to something wider. Different tools default differently and the mismatch is invisible in the configuration file.
Examples
# pin one address to a specific next hop
ip route add 192.0.2.55/32 via 10.0.0.9
# a single-address allowlist entry
allow tcp 443 from 203.0.113.7/32Things that catch people out
- A /32 route beats a /24 route to the same address, which is what makes it useful and also what makes a forgotten /32 very hard to find when traffic goes somewhere unexpected.
- The subnet calculator reports 1 usable host for a /32. There is no network address and no broadcast address to subtract, because there is no subnet.
Try it: IP Subnet Calculator
Enter any IPv4 address with a prefix or a dotted mask and get the network address, broadcast address, wildcard mask, usable host range, address class, and the hex and binary forms.
IP Subnet Calculator
LOCAL · Browser-OnlyCalculate IP subnet details, network ranges, and CIDR notation
192.168.1.0192.168.1.255255.255.255.00.0.0.255192.168.1.0/24192.168.1.1 - 192.168.1.254192.168.1.1192.168.1.254256254C0xC0A8016411000000.10101000.00000001.01100100Split into two /25 subnets
Dividing 192.168.1.0/24 one prefix deeper.
Common Subnet Masks
Related IPv4 subnets
All ipv4 subnets →What a /31 subnet is: a point-to-point link with no waste
A /31 uses the mask 255.255.255.254 and gives 2 usable addresses. What it is for and where it goes wrong.
What a /0 subnet is: the default route
A /0 uses the mask 0.0.0.0 and gives 4,294,967,294 usable addresses. What it is for and where it goes wrong.
What a /30 subnet is: a point-to-point link
A /30 uses the mask 255.255.255.252 and gives 2 usable addresses. What it is for and where it goes wrong.
What a /4 subnet is: the multicast block
A /4 uses the mask 240.0.0.0 and gives 268,435,454 usable addresses. What it is for and where it goes wrong.
What a /8 subnet is: a full class A block
A /8 uses the mask 255.0.0.0 and gives 16,777,214 usable addresses. What it is for and where it goes wrong.
What a /10 subnet is: the carrier-grade NAT block
A /10 uses the mask 255.192.0.0 and gives 4,194,302 usable addresses. What it is for and where it goes wrong.
Tools for this
- IP Subnet Calculator Free online IP subnet calculator - calculate IP subnet details, CIDR notation, and network address ranges
- IP Address Lookup Free online IP address lookup - find your public IP address and basic network information
- Number Base Converter Free online number base converter - convert numbers between decimal, binary, octal, and hexadecimal