Inside Macintosh: Open Transport /

Chapter 10 - AppleTalk Addressing

About AppleTalk Addressing

Because AppleTalk assigns node IDs dynamically whenever a node joins the network or is rebooted (although AppleTalk remembers which node ID the node last used and attempts to reclaim it), a node's address on an AppleTalk network can change from time to time. Applications cannot assume that the physical address of an AppleTalk endpoint is stable, and therefore a reliable mapping of user names to physical addresses is very important for AppleTalk.

The Name-Binding Protocol (NBP) provides a mapping of logical names (like those in the Chooser) to physical socket addresses in such a way that if the node ID changes, you can continue to reliably identify your application. An endpoint's logical name is its NBP name, also sometimes called its entity name. You can access information about your endpoint's logical addressing through an NBP-configured mapper provider, which you can also use to locate other endpoints on the network. Because AppleTalk supports dynamic name registration, NBP mapper providers can use the Open Transport name registration and deletion functions as well as the other mapper functions.

When you bind an AppleTalk endpoint, Open Transport associates the endpoint with a protocol address, which can be in one of these formats:

• The DDP address supplies the physical network address of an endpoint.
• The NBP address supplies the user-friendly NBP name.
• The combined DDP-NBP address combines the endpoint's physical network address and its NBP name.
• The multinode address supplies the physical network address of a multinode endpoint.

The following several sections discuss each address format in more detail.

Note

Open Transport also provides a generic name format (indicated by the constant kOTGenericName and the OTAddress structure). However, AppleTalk functions do not validate addresses in this form, so there is no error checking if it is not a valid address.