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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.