Multicast DNS is one of the features of Bonjour (formerly "Rendezvous"), included in Mac OS X 10.2 or later. It allows you to connect via Internet protocol (IP) to other computers on a local network by name, rather than a numbered address.
On the Internet at large, a DNS name such as "www.apple.com" must be resolved to a numbered IP address before your computer can connect to the server. A domain name system (DNS) server normally provides this name resolution service for your computer. Your Internet service provider or network administrator normally provides a local DNS server for your use.
Conversely, Multicast DNS allows computers on a local network, such as home or small office, to look up each others' names and addresses without a DNS server. Each computer knows its own name and responds to requests for that name automatically via IP multicast.
Anywhere that a you could normally use a DNS name such as "www.apple.com", you could instead enter the Bonjour name of the computer on the local network. To indicate that the name should be looked up using local multicast instead of a standard DNS query, all Bonjour host names end with the extension ".local." This helps avoid confusion between names that are local Bonjour computer names ("mycomputer.local") and globally unique DNS names ("www.apple.com").
If you use local Bonjour computer names frequently and do not want to explicitly type ".local." every time, then this extension may be added to the Search Domains field in the Network preference pane. Click the TCP/IP tab in the Network preference pane to access the Search Domains field. Be sure you have selected the correct network port from the Show menu.
For more information about setting your Bonjour Name in Mac OS X 10.2, see technical document 106964, "
Mac OS X 10.2: About Your Computer's Bonjour Name".
For more information about Multicast DNS in general, see the Multicast DNS website (
http://www.multicastdns.org/).
Note: If you have set up a private DNS server that resolves names in the .local domain, computers using Mac OS X 10.2 will not use the DNS server to resolve these names. This may result in unexpected failures to connect to hostnames defined by your server. You should use a different domain, such as .home, .office, or .lan for DNS on private networks.