First Host Calculator
Find the first usable host address in an IP subnet.
Inputs
First Usable Host
192.168.10.1
Network Address
192.168.10.0
Prefix
/24
Step by step
Network address
192.168.10.0
= 3232238080
Add 1 for first host
192.168.10.0 + 1
= 192.168.10.1
How it works
The first usable host address in a subnet is simply the network address plus one. The network address itself is reserved to identify the subnet, so the next sequential address is the first one assignable to a device.
Formula
First host
first_host = network_address + 1
- network_address
- The subnet's base address (all host bits zero)
Frequently Asked Questions
What about /31 subnets?
RFC 3021 allows both addresses in a /31 subnet to be used as host addresses on point-to-point links, since neither broadcast nor a separate network address is needed between exactly two devices.
Is the first host always the default gateway?
By convention many administrators assign the first (or last) usable address to the default gateway, but this is a convention, not a requirement — the gateway can be any valid host address in the subnet.