SAP for IPX

The Novell NetWare Service Advertising Protocol (SAP) for IPX provides a name resolution mechanism for clients to resolve the addresses of services on an IPX internetwork. Through SAP, service-providing hosts, such as file servers, print servers, and application servers advertise their service names, service types, and IPX internetwork addresses using broadcasts. The service and IPX internetwork address information is collected in a database called a SAP table by IPX routers and Novell NetWare servers.

The SAP table information is periodically advertised and propagated throughout the internetwork, in a way similar to that in which IPX routes are announced. Services are added and removed from the SAP table dynamically: they are added and maintained in the SAP table based on periodic announcements, and they are removed from the SAP table through a time-out mechanism when announcements are no longer received. To reduce convergence time, SAP uses split horizon and triggered updates. For information about split horizon and triggered updates, see "Unicast IP Routing" in this book.

SAP for IPX consists of the following types of messages:

• SAP clients such as workstations request the name and address of the nearest server of a specific type by broadcasting a SAP GetNearestServer request.
• Routers or SAP clients request the names and addresses of all services or of all services of a specific type by broadcasting a SAP general service request.
• Routers respond to SAP GetNearestServer or SAP general service requests.
• Routers periodically (every 60 seconds by default) broadcast their SAP tables using split horizon.
• Service-providing hosts that are not routers periodically (every 60 seconds by default) broadcast their services.
• Routers perform a triggered update broadcast to inform neighboring routers of a change in the SAP table.

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