The IP address, something like 192.168.0.10, is used to address an IP endpoint. The IP address is typically used to address a single network interface card (NIC). Every NIC used to communicate through IP, must have at least one IP address.
One machine can have a lot of IP addresses, as a machine can have more than one NIC, and a NIC can have more than one IP address (however, that's not widely used).
IP address classes
- 0.1.0.0 - 126.96.36.199 Class A
- 188.8.131.52 - 184.108.40.206 Class B
- 220.127.116.11 - 18.104.22.168 Class C
- 22.214.171.124 - 126.96.36.199 Class D
- 240.0.0.0 - 247.255.255.255 Class E
Special IP addresses
- 127.0.0.0 - 127.255.255.255 local loopback, should never appear on the network
169.254.0.0 - 169.254.255.254 link local for use with Automatic Private IP Addressing (APIPA)
188.8.131.52 - 184.108.40.206 multicasting RFC1112, transmission to a host group
- 255.255.255.255 limited broadcast, send to all nodes
Private IP Addresses
The following IP addresses should be used for private networks:
- 10.0.0.0 - 10.255.255.255 private in Class A
- 172.16.0.0 - 172.31.255.255 private in Class B
- 192.168.0.0 - 192.168.255.255 private in Class C
Stupid Tricks Involving IP Addresses
Most operating systems let you specify an IP address as an integer as opposed to the traditional dotted-quad format. For instance, the following commands are equivalent:
ping 192.168.5.1 ping 0xc0a80501 # Hexadecimal ping 3232236801 # Decimal ping 030052002401 # Octal
RFC1166 "INTERNET NUMBERS" list of assigned IP addresses is a very out-of-date list of IP address ranges. To find out to whom an IP address belongs, you can use various "WHOIS" services:
Latin America and Caribbean: Latin American and Caribbean Internet Addresses Registry (LACNIC) WHOIS site.
RFC1918 Private IP addresses
RFC3330 Special-Use IPv4 Addresses
My IP Tool Quickly detect your local and public IP Addresses. Firefox extension.
What about IPv6? See, for example, RFC 2373. - Guy Harris