Subnet calculator
Enter an IPv4 or IPv6 address with a prefix and read the network, the range and the host count. Check a second address, or split the block into smaller prefixes.
- IPv4 and IPv6
- Free, no sign-up
A mask in the second box replaces the prefix on the address.
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How to use it
- Enter an address and a prefix, such as 192.168.1.10/24 or 2001:db8::/32.
- Read the network, the range, the counts and the kind of address.
- Add another address to see whether it sits inside, or split the block.
IPv4 masks and IPv6 prefixes
An IPv4 prefix can be written as /24 or as a dotted mask such as 255.255.255.0. The mask has to be a run of 1s followed by a run of 0s. A /24 of 192.168.1.10 is the network 192.168.1.0, broadcast 192.168.1.255, hosts .1 to .254, 256 addresses and 254 hosts. A /32 is a single address. A /31 has two addresses and both can be used on a point-to-point link. Private, loopback, link-local, shared, multicast and public are named from the address. The old class A to E label is shown as history. The prefix is what routing uses.
IPv6 takes a prefix from 0 to 128. The page shows the compressed address, the expanded form, and the first and last address. IPv6 has a first and a last address, and the host count is the address count. A /64 names the all-zero interface id as the subnet-router anycast address. A zone id such as %eth0 is noted and left out of the prefix. Leading zeros in an IPv4 octet are read as decimal.
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Questions
What does 192.168.1.10/24 include?
The network 192.168.1.0, the broadcast 192.168.1.255, and the hosts 192.168.1.1 through 192.168.1.254. That is 256 addresses and 254 hosts.
How is a /31 different?
A /31 has two addresses and both can be used on a point-to-point link. A /32 is the single address you typed.
How does IPv6 count hosts?
The host count is the address count. The range runs from the network address through the last address. A /64 of 2001:db8:1:: is a documentation prefix with 2^64 addresses.
Can I split a block?
Choose a longer prefix. A /24 split into /26 is four blocks, and the page lists them. A mask you type in the second box replaces the prefix on the address.