An NVE is an AppleTalk network-addressable service, such as a socket. NVEs are associated with one or more entity names and attribute lists. Named NVEs are associated with network addresses through the process of name binding. Name binding can be done when the user node is first started up, or dynamically, immediately before first use. NBP orchestrates the name binding process, which includes name registration, name confirmation, name deletion, and name lookup.
Zones allow name lookup in a group of logically related nodes.
To look up names within a zone, an NBP lookup request is sent to a local router, which sends a broadcast request to all networks that have nodes belonging to the target zone. ZITs are stored in routers, which are the primary users of ZIP, but end nodes use ZIP during the startup process to choose their zone and to acquire internetwork zone information. ZIP uses RTMP routing tables to keep up with network topology changes. When ZIP finds a routing table entry that is not in the ZIT, it creates a new ZIT entry. The connection is called a tunnel , which functions as a single, virtual data link between the AppleTalk internetworks, as shown in Figure 25-6 .