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Bonjour

Bonjour is an implementation of the IETF ZeroConf working draft. Bonjour has three basic parts:

• IP assignment

• Multicast DNS

• Service discovery

You can see the first part, IP assignment, simply by plugging two computers together using a crossover cable and setting them up to use DHCP to obtain an address. Upon failing to obtain an address, the computers choose an IP number randomly from within the range reserved for ZeroConf numbers, then ARP to see if anyone has that address already, repeating this process as needed until a free address is found. This means that a relatively large number of machines can choose their own IP numbers without any administration.

Multicast DNS is a service that allows you to look up the ZeroConf IP number assigned to a particular machine without an established DNS infrastructure. Your computer sends out a request using IP multicast, asking who responds for a particular host name. The host in question then responds. That host could be a computer, a printer, or any other device that might reasonably exist on an IP-based network.

Service discovery is a way to query local machines (using multicast DNS) or a DNS server to see what machines (computers, printers, and so on) support a given service. If you are writing a service, you can register the service using Bonjour. Then anyone else who makes a request sees that your machine supports that service.

The service discovery portion of Bonjour is independent of the IP assignment portion. Thus, Bonjour can also be used for service discovery on a more traditional, configured IP network.

For more information about Bonjour, see DNS Service Discovery Programming Guide.

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