IPCalc

This application allows you to calculate the attributes of any local network, such as sub-mask, broadcast address, the range of IP addresses.
Just enter an IP and subnet mask and you will get all information related to that local network in decimal, binary and hexadecimal formats.
Besides that you can learn about:
- IPv4 networking
- TCP/IP
- CIDR (Classless Inter-Domain Routing)
- VLSM (Variable Length Subnet Masking)
- NAT (Network Address Translation)
- DHCP (Dynamic Host Configuration Protocols)
- ICMP (Internet Control Message Protocol)
- address ranges
- overview of IPv6 and much more with the included tutorial.