IIS 6: The Complete Reference

Addressing in TCP/IP

Two types of addresses are important in TCP/IP: MAC addresses and IP addresses. We'll talk about transport layer (TCP and UDP) information in the section 'The TCP, UDP, and ICMP Protocols' later in this chapter.

MAC Addresses

MAC addresses reside at the data link layer of the OSI model. The Institute of Electrical and Electronics Engineers (IEEE) assigns these addresses. Every network device has a MAC address, and every MAC address is completely unique (theoretically).

MAC addresses use a 48-bit address space, which allows for millions upon millions of MAC addresses to be used on the Internet. MAC addresses have two parts: The first 24 bits are the manufacturer ID. Each manufacturer has its own prefix. That manufacturer assigns addresses, called station IDs, using the second 24 bits.

IP Addresses

IP addresses reside at the network layer of the OSI model. The Internet Assigned Numbers Authority (IANA) assigns these addresses and has delegated large blocks to several different authorities.

IP is considered a routable protocol, because IP addresses consist of the following two parts:

• Network number This is the first portion of the IP address that identifies the address of the devices on the network that are considered part of the same group.

• Node number This is the last portion of the IP address. It identifies the individual device on that network.

  Note

  A subnet mask defines the break from network number to node number in an IP address. To see the relationship at its most basic level, you have to represent the IP address and Subnet Mask in binary numbers.