ipcalc
This is the ipv6 capable continuation of the subnet calculator from http://jodies.de/ipcalc.
> ipcalc 192.168.1.1/24 Address: 192.168.1.1 11000000.10101000.00000001. 00000001 Netmask: 255.255.255.0 = 24 11111111.11111111.11111111. 00000000 Wildcard: 0.0.0.255 00000000.00000000.00000000. 11111111 => Network: 192.168.1.0/24 11000000.10101000.00000001. 00000000 HostMin: 192.168.1.1 11000000.10101000.00000001. 00000001 HostMax: 192.168.1.254 11000000.10101000.00000001. 11111110 Broadcast: 192.168.1.255 11000000.10101000.00000001. 11111111 Hosts/Net: 254 Class C, Private Internet > ipcalc fde6:36fc:c985:0:c2c1:c0ff:fe1d:cc7f 64 Address: fde6:36fc:c985::c2c1:c0ff:fe1d:cc7f 1111110111100110:0011011011111100:1100100110000101:0000000000000000:1100001011000001:1100000011111111:1111111000011101:1100110001111111 Netmask: 64 1111111111111111:1111111111111111:1111111111111111:1111111111111111:0000000000000000:0000000000000000:0000000000000000:0000000000000000 Prefix: fde6:36fc:c985::/64 1111110111100110:0011011011111100:1100100110000101:0000000000000000:0000000000000000:0000000000000000:0000000000000000:0000000000000000