CIDR prefix
/31
255.255.255.254
2 usable hosts · 2 addresses
The mask for /31 is 255.255.255.254 — 2 addresses, 2 usable hosts. RFC 3021 point-to-point — both addresses usable, no broadcast.
Mask
255.255.255.254
Wildcard
0.0.0.1
Addresses
2
Hosts
2
Worked example: 192.168.0.0/31
Network address192.168.0.0/31
Broadcast address—
First host192.168.0.0
Last host192.168.0.1
FAQ — /31
What is the subnet mask for /31?
The subnet mask for /31 is 255.255.255.254 (wildcard: 0.0.0.1). The first 31 bits are the network part, the remaining 1 are the host part.
How many hosts fit in a /31?
A /31 block holds 2 addresses and per RFC 3021 both are usable on point-to-point links — there is no broadcast address.
How many /31 subnets fit in a /24?
A /24 network divides into 128 /31 subnets.
What is a /31 used for?
RFC 3021 point-to-point — both addresses usable, no broadcast.