The kpropd.acl file on a slave KDC provides a list of host principal names, one name per line, that specifies the systems from which the KDC can receive an updated database through propagation. If the master KDC is used to propagate all the slave KDCs, the kpropd.acl file on each slave needs to contain only the host principal name of the master KDC.
However, the Kerberos installation and subsequent configuration steps in this book instruct you to add the same kpropd.acl file to the master KDC and the slave KDCs. This file contains all the KDC host principal names. This configuration enables you to propagate from any KDC, in case the propagating KDCs become temporarily unavailable. And, by keeping an identical copy on all KDCs, you make the configuration easy to maintain.