Subnet Calculator

The number of available network and host addresses are derived from the number of bits used for subnet masking. CIDR notation is a compact representation of an IP address and its associated routing prefix.




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A broadcast address is a logical address at which all devices connected to a multiple-access communications network are enabled to receive datagrams.
A message sent to a broadcast address is typically received by all network-attached hosts, rather than by a specific host

For example A /24 network may be divided into the following subnets by increasing the subnet mask successively by one bit. This affects the total number of hosts that can be addressed in the /24 network

Prefix size Subnet mask Available
subnets
Usable hosts
per subnet
Total
usable hosts
/24 255.255.255.0 1 254 254
/25 255.255.255.128 2 126 252
/26 255.255.255.192 4 62 248
/27 255.255.255.224 8 30 240
/28 255.255.255.240 16 14 224
/29 255.255.255.248 32 6 192
/30 255.255.255.252 64 2 128
/31 255.255.255.254 128 *

 

The following special addresses and networks exist in IPv4:

0.0.0.0 the "ANY" address that is used by programs to speak to all network interfaces, it is never used directly. The whole network 0.*.*.* is reserved for special purposes (like DHCP).
10.*.*.*
172.16.*.* - 172.31.*.*
192.168.*.*
RFC Definend private address
127.0.0.1 is the localhost address The entire 127.*.*.* network is reserved for (host-)local networking.
169.254.*.* Link-Local addresses. These are automatically generated by some operating systems and (e.g. MacOS and Linux with Avahi installed) and are only usable for local communication in the LAN segment.
198.18.*.* - 198.19.*.* Network benchmark tests, this should never be used in production networks.
198.51.100.*
203.0.113.*
TEST-NET-2, Documentation and examples
TEST-NET-3, Documentation and examples
224.*.*.* Multicasts (former Class D network) - e.g. there is no default gateway or broadcast for multicasting
240.0.0.0/4 Reserved (former Class E network)
255.255.255.255 Link Broadcast - this is sent to all hosts on the same network link, but does not cross routers