SAs are required to register with all DAs that support their scopes. A DA can appear after slpd has performed active discovery. If the DA supports slpd scopes, the SLP daemon registers all advertisements on its host with the DA.
One way slpd discovers DAs is by the initial unsolicited advertisement a DA sends when it boots. The SLP daemon uses the periodic unsolicited advertisement (the heartbeat) to determine whether a DA is still active. If the heartbeat fails to appear, the daemon removes the DAs the daemon uses and those the daemon offers to UAs.
Finally, when a DA undergoes a controlled shutdown, it transmits a special DA advertisement that informs listening SA services that it will be out of service. The SLP daemon also uses this advertisement to remove inactive DAs from the cache.
If your network is subject to frequent partitions and SAs are long-lived, slpd can remove cached DAs during the partitioning if heartbeat advertisements are not received. By decreasing the heartbeat time, you can decrease the delay before a deactivated DA is restored to the cache after the partition is repaired.