3Com 2500 manual A SAP packet consists of the following fields

6-12 CHAPTER 6: ROUTING WITH IPX

A SAP packet consists of the following fields:

■Operation — This field indicates the type of operation the SAP packet performs. It can be set to one of the following values:

1=Request

2=Response

3=Get Nearest Server Request

4=Get Nearest Server Response

■Server Entry — Each 64-byte server entry includes information about a particular server. It consists of the following fields:

■Service Type — This 2-byte field identifies the type of service the server provides.

Although IPX routers use SAP, routers typically do not act as servers and require no Service Type assignment.

■Server Name — This field contains the 48-byte character string name that is assigned to a server. The server name, in combination with the service type, uniquely identifies a server on an internetwork.

■Network Address — This 4-byte field contains the server’s network address.

■Node Address — This 6-byte field contains the server’s node address.

■Socket Address — This 2-byte field contains the socket number that the server uses to receive service requests.

■Hops to Server — This 2-byte field indicates the number of intermediate networks that must be passed through to reach the server associated with this field entry. Each time the packet passes through an intermediate network, the field is incremented by 1.

By using SAP, servers can advertise their services and addresses. The information that these servers broadcast is not directly used by clients; rather it is collected by a SAP agent within each router on the server’s segment. The SAP agents store this information in a server information table. If the agents reside within a server, the information is also stored in their server’s bindery. The clients can then contact the nearest router or file server SAP agent for server information.