Zero Configuration Networking: The Definitive Guide

Chapter 3. Names Without DNS

In Chapter 2, you saw how Zeroconf allows your device to obtain a locally unique IP address without a DHCP server or a network administrator. The next step is to obtain a name that can resolve to this address. The method you use to do that is independent of how you have obtained your IP address; for example, you may have taken advantage of link-local addressing, been assigned an address using DHCP, or manually assigned an IP address. If you need a name that is at least locally unique and there is no DNS server available, the Multicast DNS (mDNS) mechanism will help you obtain one.

This stage may feel unnecessary. After all, why not just use the IP address obtained in the last step as the device name? IP addresses may change over time, and network location and IP addresses are not a convenient form for people to remember or recognize devices. In other words, you need to assign locally unique names and not use the automatically assigned IP addresses for the following reasons:

• The IP address provided may be temporary . If you are communicating with a device at a given address, it is quite possible that, at a later time, the device may have a different address. Attempting to contact the device by connecting to its old address will not succeed. Even worse, that address could be reused by a different device, so when you attempt to connect to it, you may apparently succeed, except you’re not actually communicating with the device you intended.

• With mobile devices ...