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The TCP/IP Guide  9  TCP/IP Lower-Layer (Interface, Internet and Transport) Protocols (OSI Layers 2, 3 and 4)       9  TCP/IP Internet Layer (OSI Network Layer) Protocols            9  Internet Protocol (IP/IPv4, IPng/IPv6) and IP-Related Protocols (IP NAT, IPSec, Mobile IP)                 9  Internet Protocol Version 4 (IP, IPv4)                      9  IP Addressing                           9  IP Addressing Concepts and Issues

IP Addressing Concepts and Issues 1 2 3 IP Address Size, Address Space and "Dotted Decimal" Notation

IP Address Datagram Delivery Issues

In a physical network such as an Ethernet, the MAC address is all the information needed to send data between devices. In contrast, an IP address represents only the final delivery point of the datagram. The route taken depends on the characteristics of the network paths between the source and destination devices. It is even possible that there may not be a route between any two devices, which means two devices cannot exchange data even if they know each other's addresses!

There are two distinct ways that a network can be set up with IP addresses. On a private network a single organization controls the assignment of the addresses for all devices; they have pretty much absolute control to do what they wish in selecting numbers as long as each address is unique. In contrast, on a public network a mechanism is required to ensure both that organizations don't use overlapping addresses and also to enable efficient routing of data between organizations. The best-known example of this is of course the Internet, where public IP registration and management facilities have been created to address this issue. There are also advanced techniques now such as IP Network Address Translation that allow a network using private addresses to be interfaced to a public TCP/IP network.

There are two basic ways that IP addresses can be configured. In a static configuration setup, each device is manually configured with an IP address that doesn't change. This is fine for small networks but quickly becomes an administrative nightmare in larger networks when changes are required. The alternative, dynamic configuration, allows IP addresses to be assigned to devices and changed under software control. The two host configuration protocols, BOOTP and DHCP, were created to fill this latter function.

Provision is included in the IP addressing scheme for all three basic types of addressing.

The topics that follow in this section, and the other sections in our discussion of IP, expand upon these concepts with more particulars.

IP Addressing Concepts and Issues 1 2 3 IP Address Size, Address Space and "Dotted Decimal" Notation