IPv4
From FreeBSDwiki
Internet Protocol version 4. Wherein unique addresses are assigned to devices (viz, computers) in a series of four numbers (called octets) seperated by decimals, like so:
216.239.57.99
That particular number corresponds to google.com. There are reserved addresses that are not routable -- notably 127.0.0.1, 172.16.0.0/16, 192.168.0.0/16, and 10.0.0.0/8. These addresses are reserved for local networks and will never be routable beyond them.
The world is running out of IPv4 addresses, so it will eventually switch over to IPv6. The current work-around has been to use NAT
