During server installation, the
ipa-server-install command by default automatically assigns a random current ID range to the installed server. The setup script randomly selects a range of 200,000 IDs from a total of 10,000 possible ranges. Selecting a random range in this way significantly reduces the probability of conflicting IDs in case you decide to merge two separate IdM domains in the future.
However, you can define a current ID range manually during server installation by using the following two options with
--idstart gives the starting value for UID and GID numbers; by default, the value is selected at random,
--idmax gives the maximum UID and GID number; by default, the value is the
--idstart starting value plus 199,999.
If you have a single IdM server installed, a new user or group entry receives a random ID from the whole range. When you install a new replica and the replica requests its own ID range, the initial ID range for the server splits and is distributed between the server and replica: the replica receives half of the remaining ID range that is available on the initial master. The server and replica then use their respective portions of the original ID range for new entries. Also, if less than 100 IDs from the ID range that was assigned to a replica remain, meaning the replica is close to depleting its allocated ID range, the replica contacts the other available servers with a request for a new ID range.
A server receives an ID range the first time the DNA plug-in is used; until then, the server has no ID range defined. For example, when you create a replica from a master server, the replica does not receive an ID range immediately. The replica requests an ID range from the initial master only when the first ID is about to be assigned on the replica.
If the initial master stops functioning before the replica requests an ID range from it, the replica is unable to contact the master with a request for the ID range. An attempt to add a new user on the replica fails. In such situations, you can find out what ID range is assigned to the disabled master and assign an ID range to the replica manually, which is described in Section 14.5, “Manual ID Range Extension and Assigning a New ID Range”