How many usable hosts are in a /24?

254 — the network address (first IP) and broadcast address (last IP) are reserved. For a /n subnet, usable hosts = 2^(32-n) - 2.

What's a wildcard mask?

The bitwise inverse of a subnet mask, used in Cisco ACLs and OSPF configurations. For a /24 (mask 255.255.255.0), the wildcard is 0.0.0.255.

Yes — enter an IPv6 prefix (2001:db8::/32) to get expanded notation, address count, and first/last address in the block.

CIDR subnet calculator with utilities. Part of the DevTools Surf developer suite. Browse more tools in the Networking collection.

Calculate the usable IP range, network address, and broadcast address for any CIDR block.
Plan IP addressing for a new office network with multiple VLANs.
Determine if two IP addresses are on the same subnet given a mask.
Find the smallest CIDR block that contains a given range of IP addresses.

Enter CIDR notation (192.168.1.0/24) to get all derived values at once — network address, broadcast, first/last host, and total host count.
Use the subnet divider to split a /24 into multiple smaller subnets for VLAN planning.
Check the wildcard mask output when configuring Cisco ACLs — wildcard masks are the bitwise inverse of subnet masks and are required in access-list commands.

CIDR (Classless Inter-Domain Routing) was introduced in 1993 (RFC 1518/1519) to replace the Class A/B/C system, which had nearly exhausted IPv4's address space. CIDR allowed flexible prefix lengths instead of fixed 8/16/24-bit classes.
IPv4 has approximately 4.3 billion addresses (2^32). The last unallocated /8 block was assigned by IANA to regional registries in February 2011. IPv6 has 340 undecillion addresses (2^128) — enough to assign 7×10^28 addresses to every person alive.
The RFC 1918 private address ranges (10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16) were allocated in 1996 as non-routable address space. NAT was invented specifically to allow these private addresses to share a single public IP.

How many usable hosts are in a /24?: 254 — the network address (first IP) and broadcast address (last IP) are reserved. For a /n subnet, usable hosts = 2^(32-n) - 2.
What's a wildcard mask?: The bitwise inverse of a subnet mask, used in Cisco ACLs and OSPF configurations. For a /24 (mask 255.255.255.0), the wildcard is 0.0.0.255.
Does it support IPv6?: Yes — enter an IPv6 prefix (2001:db8::/32) to get expanded notation, address count, and first/last address in the block.

CIDR subnet calculator with utilities. Part of the DevTools Surf developer suite. Browse more tools in the Networking collection.

Calculate the usable IP range, network address, and broadcast address for any CIDR block.
Plan IP addressing for a new office network with multiple VLANs.
Determine if two IP addresses are on the same subnet given a mask.
Find the smallest CIDR block that contains a given range of IP addresses.

Enter CIDR notation (192.168.1.0/24) to get all derived values at once — network address, broadcast, first/last host, and total host count.
Use the subnet divider to split a /24 into multiple smaller subnets for VLAN planning.
Check the wildcard mask output when configuring Cisco ACLs — wildcard masks are the bitwise inverse of subnet masks and are required in access-list commands.

CIDR (Classless Inter-Domain Routing) was introduced in 1993 (RFC 1518/1519) to replace the Class A/B/C system, which had nearly exhausted IPv4's address space. CIDR allowed flexible prefix lengths instead of fixed 8/16/24-bit classes.
IPv4 has approximately 4.3 billion addresses (2^32). The last unallocated /8 block was assigned by IANA to regional registries in February 2011. IPv6 has 340 undecillion addresses (2^128) — enough to assign 7×10^28 addresses to every person alive.
The RFC 1918 private address ranges (10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16) were allocated in 1996 as non-routable address space. NAT was invented specifically to allow these private addresses to share a single public IP.

How many usable hosts are in a /24?: 254 — the network address (first IP) and broadcast address (last IP) are reserved. For a /n subnet, usable hosts = 2^(32-n) - 2.
What's a wildcard mask?: The bitwise inverse of a subnet mask, used in Cisco ACLs and OSPF configurations. For a /24 (mask 255.255.255.0), the wildcard is 0.0.0.255.
Does it support IPv6?: Yes — enter an IPv6 prefix (2001:db8::/32) to get expanded notation, address count, and first/last address in the block.