How To Use CIDR Calculator
- Input IP address. Incomplete IP addresses will be automatically finished with zeros if necessary;
- Invalid IP addresses will appear read and will show no calculation results;
- Select CIDR netmask or related parameter - max networks or addresses;
- CIDR calculator will calculate CIDR notation, wildcard mask, maximum subnets and addresses, and CIDR address range;
- Calculator can be used to plan set up of large or medium networks or for the studying.
About CIDR Calculator
CIDR calculator is used to calculate different network parameters (IP route, broadcast, address range etc.) when classless inter-domain routing method of allocating IP addresses and routing IP packets is being used. Classful method was replaced by CIDR back in 1993 and the motivation was a necessity to reduce the growth of routing tables and to use IPv4 address pool more effectively. For classful IP address calculations, please use Subnet calculator.
Classless inter-domain routing is based on VLSM (variable length subnet mask). It allows networks to be divided into different size and type subnets while not wasting any of the IP addresses. For example, network 192.168.1.0/24 can be divided into two /26 and one /25 subnets - 192.168.1.0/26, 192.168.1.64/26 and 192.168.1.128/25. Reversed process of splitting networks into variable length subnet mask subnets is called supernetting. To calculate supernets please use Supernet calculator
More detailed information about VLSM can be found in RFC 950.
CIDR mask (routing prefix) shows what part of an IP address is network part and which is a host part. CIDR mask in IP version 4 is 32 bits long and is usually represented using dotted decimal form. Valid CIDR masks binary form starts with single or multiple ones (ones part) followed by stream of zeros (zeros part). After first zero there can only be ones. For example, 11111111.11111111.11110000.00000000 (255.255.240.0).
Maximum number of subnets available for the specified CIDR mask. It calculated by: 232-routing_prefix
Maximum number of addresses available for the specified CIDR mask.It calculated by: 232-routing_prefix - 2. Exception are networks with "/32" masks: 232-routing_prefix.
CIDR notation is a format of IP address and the routing prefix. This format consists of network ID calculated from IP address and CIDR mask and from CIDR mask itself as a routing prefix (for example, 10.5.100.0/24 or 10.5.100.0/255.255.255.0). CIDR notation is also used for IPv6 routing.
Wildcard mask is inverted CIDR mask and it is calculated by performing a bitwise NOT on CIDR mask:
NOT 11111111.11111111.11111111.00000000 (255.255.255.0) = 00000000.11111111.11111111.11111111 (0.255.255.255)
CIDR Address Range
Range of addresses that selected IP address and subnet mask covers. The first is calculated by add 1 to network ID and last is calculated by subtracting 1 from broadcast.