In terms of managing addresses on for the public internet, there are a set of address ranges which one should never see... publically. Privately, that is, within someone's local network, they can be seen, are seen, and should be seen.
- 0.0.0.0/8: not seen as an address but as a default route.
- 10.0.0.0/8: a common internal rfc 1918 range.
- 127.0.0.0/8: localhost addresses, ie, loopbacks on individual machines, with 127.0.0.1 the most common. I've used addional
addresses for setting proxy forwarding with ssh port forwarding configurations
- 169.254.0.0/16: rfc 3927 for internal networks without dhcp and no addressing
structure
- 172.16.0.0/12: a common internal rfc1918 range.
- 192.0.2.0/24: rfc 3330 for documentation and example code
- 192.168.0.0/16: a common internal rfc1918 range.
- 198.18.0.0/15: rfc 2544 network benchmark tests
- 223.0.0.0/8: reserved
- 224.0.0.0/3: multicasting
More information on IPv4 addressing can be found at Wikipedia.