Why does a /24 have 254 hosts, not 256?

The network address (all host bits 0) and the broadcast address (all host bits 1) cannot be assigned to hosts. 256 total minus 2 reserved equals 254 usable.

RFC 3021 defines /31 for point-to-point links: both addresses are usable hosts, no broadcast. A /32 is a single host, used by loopback interfaces and route advertisements.

What is a wildcard mask?

The bitwise inverse of the netmask. Cisco ACLs expect wildcard masks instead of netmasks — the tool shows both so you can copy whichever your config needs.

Subnet Calculator

IPv4 CIDR

Try 10.0.0.0/8, 172.16.5.100/20, or 198.51.100.42/27. Math runs locally in your browser.

Network

192.168.1.0/24

254 usable hosts · 256 total addresses · Class C

Netmask

255.255.255.0

Wildcard

0.0.0.255

First host

192.168.1.1

Last host

192.168.1.254

Broadcast

192.168.1.255

Prefix

/24

Binary mask

11111111.11111111.11111111.00000000

How to use the subnet calculator

Type any IPv4 address followed by a slash and a prefix length — for example 192.168.1.0/24. The calculator derives every field from that one input as you type.

The network address is the first address in the range and cannot be assigned to a host. The broadcast address is the last address and also cannot be assigned. Every address between them is usable, which is why a /24 has 254 hosts (256 − 2) rather than 256.

Two special cases: /31 is defined by RFC 3021 for point-to-point links and treats both addresses as usable (2 hosts, no broadcast). /32 describes a single host.

The wildcard mask is the bitwise inverse of the netmask and is what Cisco ACLs expect. The class is the legacy classful assignment based on the first octet — informational only since classless routing (CIDR, 1993) replaced it. The RFC 1918 private range indicator tells you whether the block is from 10.0.0.0/8, 172.16.0.0/12, or 192.168.0.0/16, which are not routable on the public internet.

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Related tools

Type an IPv4 CIDR like 192.168.1.0/24 and see every derived field — network, broadcast, host range, netmask, and wildcard.