Toolman

Subnet mask 255.255.255.255

/32

255.255.255.255 · 1 usable host

CIDR prefix/32
Subnet mask255.255.255.255
Wildcard mask0.0.0.0
Binary11111111.11111111.11111111.11111111
Total addresses1
Usable hosts1

How many hosts it holds

A single address. Not a network so much as one host written in network notation, which is how a firewall rule names one machine.

Reading the mask

A subnet mask is 32 one-bits followed by 0 zero-bits, written as four decimal octets. The ones mark the part of the address that identifies the network and the zeros mark the part that identifies the host, which is why the mask is always a solid run of ones — a mask with a gap in it would split the host part in two and is not valid.

11111111.11111111.11111111.11111111
255.255.255.255

The prefix length is simply the count of those ones, so 255.255.255.255 is /32 and nothing has to be calculated to convert between them.

The wildcard, and where it turns up

Cisco access lists and OSPF network statements take a wildcard mask rather than a subnet mask — the same value with every bit inverted, 0.0.0.0 here. It trips people up because the two look alike and mean opposite things: in a subnet mask a one means "this bit is the network", and in a wildcard a one means "ignore this bit".

Frequently asked questions

What CIDR prefix is 255.255.255.255?

255.255.255.255 is /32. The mask has 32 bits set, and the prefix length is that count.

How many hosts does 255.255.255.255 allow?

A single address. Not a network so much as one host written in network notation, which is how a firewall rule names one machine.

What is the wildcard mask for 255.255.255.255?

0.0.0.0 — the mask with every bit flipped. Cisco access lists and OSPF network statements take the wildcard rather than the mask, which is the usual reason to want it.

Other masks

/32 in full · Every subnet mask · CIDR reference