All servers and routers keep a complete list of the
services available throughout the network in server information tables. Like RIP, SAP also
uses an aging mechanism to identify and remove table entries that become invalid.
By default, service advertisements occur at 60-second intervals. However, although
service advertisements might work well on a LAN, broadcasting services can require too
much bandwidth to be acceptable on large internetworks, or in internetworks linked on WAN
serial connections.
Routers do not forward SAP broadcasts. Instead, each router builds its own SAP table
and forwards the SAP table to other routers. By default this occurs every 60 seconds but
the router can use access lists to control the SAPs accepted or forwarded. 