IP Address

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 that communicates 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).

The IP address can be statically assigned to a NIC through system-specific configuration, or dynamically assigned using DHCP or APIPA.

IP address classes

• 0.1.0.0 - 126.0.0.0 Class A
• 128.0.0.0 - 191.255.0.0 Class B
• 192.0.1.0 - 223.255.255.0 Class C
• 224.0.0.0 - 239.255.255.255 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)

• 224.0.0.0 - 239.255.255.255 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

External Links

• RFC1166 "INTERNET NUMBERS" list of assigned IP addresses is a very out-of-date list of IP address ranges.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:

  • Asia: Asia Pacific Network Information Centre (APNIC) WHOIS site

  • Europe: Réseaux IP Européens (RIPE) WHOIS site Assigned IP addresses in Europe

  • Latin America and Caribbean: Latin American and Caribbean Internet Addresses Registry (LACNIC) WHOIS site.

  • United States and Canada: American Registry for Internet Numbers (ARIN) WHOIS site

• RFC1918 Private IP addresses

• RFC3330 Special-Use IPv4 Addresses

• My IP Tool Quickly detect your local and public IP Addresses. Firefox extension.

Discussion

What about IPv6? See, for example, RFC 2373. - Guy Harris