Each suffix in your directory can be placed in read-only mode independently and can return a specific referral if one is defined. Directory Server also provides a read-only mode for the server that applies to all suffixes and can return a global referral when one is defined.
The server read-only mode is designed to allow administrators to prevent modifications to the directory contents while performing tasks such as reindexing the suffixes. For this reason, server read-only mode does not apply to the following configuration branches:
These branches should be protected at all times by access control instructions (ACIs) against modifications by non-administration users, regardless of the read-only setting (see Chapter 6, Directory Server Access Control). Global read-only mode prevents update operations on all other suffixes in the directory, including update operations initiated by the Directory Manager.
Read-only mode also interrupts replication on a suffix if it is enabled. A master replica no longer has any changes to replicate, although it continues to replicate any changes that were made before read-only mode was enabled. A consumer replica does not receive updates until read-only mode is disabled. A master in a multi master replication environment does not have any changes to replicate and is not able to receive updates from the other masters.
You can use DSCC to perform this task. For information, see Directory Service Control Center Interface and the DSCC online help.