More
More
IP Subnet Calculator
CIDR ranges, masks and host counts.
Free. Runs in your browser: nothing you enter or open is uploaded.
Everything is worked out in your browser with plain arithmetic; no address you type is looked up or sent anywhere. For /31 and /32 the tool follows RFC 3021 and RFC 4632: a /31 point to point link has two usable addresses and a /32 is a single host.
How to use it
- Type an address with its prefix, such as 192.168.1.10/26, or pick the mask from the list.
- Read the network, broadcast, host range and host count, and the binary view if you want to see where the split falls.
- To divide a range, open Split a network and choose how many subnets or how many hosts each needs. IPv6 has its own tab.
Questions
Why are there two fewer usable hosts than addresses?
In a normal IPv4 subnet the first address names the network and the last is the broadcast address, so neither can be given to a device. A /26 has 64 addresses and 62 usable hosts. The exceptions are /31, used for links between two routers, and /32, a single address.
What is a wildcard mask?
The subnet mask with every bit flipped. Cisco access lists and OSPF use it: 0.0.0.63 matches the 64 addresses of a /26.
Which ranges are private?
10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16 are for private networks and are not routed on the internet. 100.64.0.0/10 is shared address space used by carrier grade NAT, and 169.254.0.0/16 is what a device gives itself when it gets no address.
Why does IPv6 not have a broadcast address?
IPv6 replaced broadcast with multicast, so every address in a prefix can be used. A /64 is the standard size for a single network, which gives about 18 quintillion addresses.