IP address is an identity of a computer or other network device on a TCP/IP network. Networks using the TCP/IP protocol route packets based on the IP address to its destination. For the most TCP/IP networks which are based on the IPv4, the format of an IP address is a 32-bit numeric address written as four numbers separated by periods. Each number can be zero to 255, for example, 25.230.10.40. The four numbers in an IP address are used in different ways to identify a particular network and a host on that network. Certain values are restricted from use as typical IP addresses. For example, the IP address 0.0.0.0 is reserved for the default network; the address 255.255.255.255 is used for broadcasts and the IP address 127.0.0.1 is used as the loopback address.
Within a private local network, you may assign any unique IP addresses to a network device. However, on the Internet, a unique and registered IP addresses, called Internet addresses, is required to avoid duplicates.
Four regional Internet registries -- ARIN, RIPE NCC, LACNIC and APNIC -- assign Internet addresses from the following three classes:
- Class A - This class is for very large networks, such as a major international company might have. IP addresses with a first octet from 1 to 126 are part of this class.
- Class B - Class B is used for medium-sized networks. IP addresses with a first octet from 128 to 191 are part of this class.
- Class C - Class C addresses are commonly used for small to mid-size businesses. IP addresses with a first octet from 192 to 223 are part of this class.
The number of unassigned Internet addresses is running out under the IPv4, so a new scheme is gradually replacing the system based on classes A, B, and C and is tied to adoption of IPv6. IPv6 uses 128-bit binary for addressing purpose. IPv6 addresses are expressed in hexadecimal format (base 16) which allows not only numerals (0-9) but a few characters as well (a-f). IPv6 addresses can now be expressed as a string of 32 visible characters. A sample ipv6 address looks like: 3ffe:ffff:100:f101:210:a4ff:fee3:9566
There is a major difference in the IP address requirements between an IPv4 node and an IPv6 node. An IPv4 node typically uses one IP address; but an IPv6 node requires more than one IP address. There are three major types of IPv6 addresses as follows:
- Unicast - An address for a single interface. A packet that is sent to a unicast address is delivered to the interface identified by that address.
- Anycast - An address for a set of interfaces that typically belong to different nodes. A packet sent to an anycast address is delivered to the closest interfaceas defined by the routing protocols in useidentified by the anycast address.
- Multicast - An address for a set of interfaces (in a given scope) that typically belong to different nodes. A packet sent to a multicast address is delivered to all interfaces identified by the multicast address (in a given scope).
The Internet Assigned Numbers Authority (IANA) is the entity to have the responsibility for the management of the IPv6 address space.
Related Terms: IPv4, IPv6, TCP/IP
Reference Links: http://www.faqs.org/rfcs/rfc3177.html: IAB/IESG Recommendations on IPv6 Address Allocations to Sites