The sipcalc utility for Linux is used to calculate subnets for IP addresses. The below example shows a /26 address and the available IP addresses and number of network nodes in the subnet. This is a good way to calculate the network mask if the network administrator requires this information to input it into a Cisco router. Instead of using binary to decimal conversion to achieve this.
ubuntu ~ $ sipcalc 172.16.0.1/26 -[ipv4 : 172.16.0.1/26] - 0 [CIDR] Host address - 172.16.0.1 Host address (decimal) - 2886729729 Host address (hex) - AC100001 Network address - 172.16.0.0 Network mask - 255.255.255.192 Network mask (bits) - 26 Network mask (hex) - FFFFFFC0 Broadcast address - 172.16.0.63 Cisco wildcard - 0.0.0.63 Addresses in network - 64 Network range - 172.16.0.0 - 172.16.0.63 Usable range - 172.16.0.1 - 172.16.0.62
Compare this with a /24 address. There are 256 addresses available instead of 64. Splitting a network into subnets allows the segregation of the network into various secure networks to separate one network from another to greatly improve network security.
ubuntu ~ $ sipcalc 172.16.0.1/24 -[ipv4 : 172.16.0.1/24] - 0 [CIDR] Host address - 172.16.0.1 Host address (decimal) - 2886729729 Host address (hex) - AC100001 Network address - 172.16.0.0 Network mask - 255.255.255.0 Network mask (bits) - 24 Network mask (hex) - FFFFFF00 Broadcast address - 172.16.0.255 Cisco wildcard - 0.0.0.255 Addresses in network - 256 Network range - 172.16.0.0 - 172.16.0.255 Usable range - 172.16.0.1 - 172.16.0.254
man sipcalc to get more information on this very useful utility.