Inside the Mac OS: A look at AppleTalk and AppleTalk zones

Computerworld - Editor's note: This is the first of a series of articles covering Mac OS X Server networking topics.
AppleTalk is one of the two protocols typically used in today's Mac networks. The other is TCP/IP, which has become the dominant network protocol for all computer networks and is the protocol on which the Internet is based.
AppleTalk is considered a routable and self-configuring protocol. Calling it a routable protocol means that AppleTalk can be used to transmit data across multiple networks with the use of a router. Self-configuring means that although you can manually assign AppleTalk addresses to computers and other devices on a network, devices capable of assigning themselves unique addresses can do so. (By contrast, TCP/IP requires some configuration, even if that configuration is done through the use of a DHCP server.)
When a computer or other device that supports AppleTalk first starts up (or when AppleTalk is enabled on a device already running), it randomly selects an address for itself and broadcasts a special series of 10 AppleTalk address resolution packets. These packets contain both a randomly selected node number (which the device will use as its AppleTalk address on the network) and a selected network number (which will be used to identify this particular LAN from any other). The network number is stored from one AppleTalk session to another and a computer will use the same network number unless told to use a different one.
If there are AppleTalk devices on the network, they respond to the packets in two ways. If the randomly selected node number is in use, a device will respond that it has already taken that node number. The new device then will pick another random number and broadcast another series of address resolution packets. This continues until the device selects a node number unique within the network, at which point it will get no response to the resolution packets. If the device is on a routed AppleTalk network, a router will respond to the network number portion of the resolution packet by supplying the appropriate network number to the device (if that number differs from the one included in the address resolution packets).

Also included in the resolution packet is the computer name, which has been designated by an administrator in the File Sharing control panel (classic Mac OS) or the Sharing pane of System Preferences (Mac OS X). This way, users of other computers will see a computer name (sometimes called an AppleTalk name) rather than a random node