dan@lindow.io:~$ sipcalc
Enter an IPv4 or IPv6 address with CIDR prefix to begin.
Example: 10.0.0.1/24 or 2001:db8::/32
Enter an IPv4 or IPv6 address with CIDR prefix to begin.
Example: 10.0.0.1/24 or 2001:db8::/32