Figure 31-3 illustrates these encapsulation types. Four IPX encapsulation types exist. Advertisements are sent via SAP every 60 seconds. A SAP operation begins when routers listen to SAPs and build a table of all known services along with their network address. Routers then send their SAP table every 60 seconds.
Novell clients can send a query requesting a particular file, printer, or gateway service.
The local router responds to the query with the network address of the requested service, and the client then can contact the service directly. SAP, however, still is required in NetWare 4.0 networks for workstations when they boot up to locate an NDS server. Using the SAP identifier, SAP advertisements can be filtered on a router's input or output port, or from a specific router. SAP filters conserve network bandwidth and are especially useful in large Novell installations where hundreds of SAP services exist. In general, the use of SAP filters is recommended for services that are not required for a particular network.