Slave servers, on the other hand, obtain a complete copy of the maps periodically from the master server. To ensure that the system information is consistent at the slave servers, and therefore throughout the whole domain, you should make all updates to the maps at the master server. Then, propagate the new maps to the slave servers. To propagate a map means to copy it from the master server to all the slave servers. Propagation eliminates the need to update each map individually.
Maps propagate automatically every few minutes if the master server is running the ypupdated daemon.
If you stop and restart NIS on the master server, all the maps will propagate to the slave servers immediately. If you enter the yppush command at the master server, the changes will propagate immediately. The yppush command notifies all slave servers that a map must be transferred. The ypserv daemon on each slave server will run the ypxfr command to get the updated map. A slave server that is out of service when you enter the yppush command retains the earlier version of the map when it returns to the network.