The sipcalc command is very useful for calculating an IP subnet. This command shows the amount of hosts available for a given subnet.
root@debian:/home/homer# sipcalc 192.168.100.1/24 -[ipv4 : 192.168.100.1/24] - 0 [CIDR] Host address - 192.168.100.1 Host address (decimal) - 3232261121 Host address (hex) - C0A86401 Network address - 192.168.100.0 Network mask - 255.255.255.0 Network mask (bits) - 24 Network mask (hex) - FFFFFF00 Broadcast address - 192.168.100.255 Cisco wildcard - 0.0.0.255 Addresses in network - 256 Network range - 192.168.100.0 - 192.168.100.255 Usable range - 192.168.100.1 - 192.168.100.254 |
You may also specify the interface that your Linux installation is using. I am using Debian 7.0 in VMware; so this shows the interface IP address as well as the one appended as a command line argument.
root@debian:/home/homer# sipcalc 192.168.100.1/24 eth0 -[ipv4 : 192.168.100.1/24] - 0 [CIDR] Host address - 192.168.100.1 Host address (decimal) - 3232261121 Host address (hex) - C0A86401 Network address - 192.168.100.0 Network mask - 255.255.255.0 Network mask (bits) - 24 Network mask (hex) - FFFFFF00 Broadcast address - 192.168.100.255 Cisco wildcard - 0.0.0.255 Addresses in network - 256 Network range - 192.168.100.0 - 192.168.100.255 Usable range - 192.168.100.1 - 192.168.100.254 - -[int-ipv4 : eth0] - 0 [CIDR] Host address - 192.168.184.129 Host address (decimal) - 3232282753 Host address (hex) - C0A8B881 Network address - 192.168.184.0 Network mask - 255.255.255.0 Network mask (bits) - 24 Network mask (hex) - FFFFFF00 Broadcast address - 192.168.184.255 Cisco wildcard - 0.0.0.255 Addresses in network - 256 Network range - 192.168.184.0 - 192.168.184.255 Usable range - 192.168.184.1 - 192.168.184.254 |
This is an example that splits an IP address into 8 subnets. This is using a 255.255.255.224 netmask.
deusexmachina ~ # sipcalc -s27 192.168.100.0/24 -[ipv4 : 192.168.100.0/24] - 0 [Split network] Network - 192.168.100.0 - 192.168.100.31 Network - 192.168.100.32 - 192.168.100.63 Network - 192.168.100.64 - 192.168.100.95 Network - 192.168.100.96 - 192.168.100.127 Network - 192.168.100.128 - 192.168.100.159 Network - 192.168.100.160 - 192.168.100.191 Network - 192.168.100.192 - 192.168.100.223 Network - 192.168.100.224 - 192.168.100.255 |
This is an easy way to calculate IP addressing for subnetting. The ipcalc command may also be used for this.
deusexmachina ~ # ipcalc -r 192.168.1.0 192.168.100.255 deaggregate 192.168.1.0 - 192.168.100.255 192.168.1.0/24 192.168.2.0/23 192.168.4.0/22 192.168.8.0/21 192.168.16.0/20 192.168.32.0/19 192.168.64.0/19 192.168.96.0/22 192.168.100.0/24 |
The above example shows how many subnets you may get with this IP range.