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Nodes and applications use NBP to discover the addresses of nodes and services such as file servers and printers. NBP maps network entity names to AppleTalk addresses. Because people usually find it easier to remember names than numerical addresses, NBP enables users to specify descriptive or symbolic names for entities that applications label with numerical addresses.
One example of how AppleTalk uses NBP is the Chooser application. Users or applications form an NBP lookup by picking a zone and the type of device or service they are interested in. These two pieces of information form an NBP lookup equivalent to the following:
I want all devices of the chosen type (for example, a file server, a mail server, or a printer) in the chosen zone (service location) to respond to me (user location) with their network addresses.
The lookup is then sent to the appropriate zone. All devices or services of the chosen type in the chosen zone respond with an NBP reply. An NBP reply, depending on the content of the lookup, contains the name, type, and network address (AppleTalk address) of the service provided by a node. Then, applications base their communications with the device on its address. In comparison, the service is related through its name. The NBP reply contains information equivalent to the following:
The names and types of services available at this network address and zone (service location) are sent back to the requesting station (the user location).
If filters have been configured for the receiving router, the router then uses the filters to determine whether each NBP reply should be dropped or forwarded.
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