When a file server or,
in the case of SCO IPX/SPX,
SAPD is first brought up, its internal SAP agent:
Places the name of the server in the agent's server information table.
Sends a SAP broadcast to each of its
directly connected segments to inform the SAP agents on those
segments that a new server has become available.
Broadcasts a request to each of its directly connected segments for
information about other servers that exist on the network.
These requests are responded to by all the SAP agents on these
directly connected segments.
Places the information
received in these responses in its server information table.
Performs broadcasts about the servers
that it is aware of every 60 seconds (except on asynchronous and X.25 links).
Figure 4-13
illustrates these initial and periodic broadcasts.
Figure 4-13 Sequence used to build and maintain the server information table
As with routing information broadcasts, all server information
broadcasts are local broadcasts and are subject to the best
information algorithm. Any changes in server information are
passed on immediately to ensure current information across the
network. The router applies the aging process to its server
information table entries in case any servers become unavailable.
Finally, if the router is brought down, it will indicate to its
directly connected segments that the servers the router has been
advertising will no longer be available.