The database that is stored on the master KDC must be regularly propagated to the slave KDCs. You can configure the propagation of the database to be incremental. The incremental process propagates only updated information to the slave KDCs, rather than the entire database. For more information about database propagation, see Administering the Kerberos Database.
If you do not use incremental propagation, one of the first issues to resolve is how often to update the slave KDCs. The need to have up-to-date information that is available to all clients must be weighed against the amount of time it takes to complete the update.
In large installations with many KDCs in one realm, one or more slaves can propagate the data so that the process is done in parallel. This strategy reduces the amount of time that the update takes, but it also increases the level of complexity in administering the realm. For a complete description of this strategy, see Setting Up Parallel Propagation.