Directory Server includes a way of promoting and demoting the replica role of a directory instance. This feature enables you to promote a replica hub to a multi-master supplier or vice versa. You can also promote a consumer to the role of replica hub and vice versa. However, you cannot promote a consumer directly to a multi-master supplier or vice versa. In this case, the consumer must first become a replica hub and then it can be promoted from a hub to a multi-master replica. The same is true in the reverse direction.
Replica role promotion is useful in distributed deployments. Consider the case when you have six geographically dispersed sites. You would like to have a multi-master supplier at each site but are limited to only one per site for up to four sites. If you put at least one hub at each of the other two sites, you could promote them if one of the other multi-master suppliers is taken offline or decommissioned for some reason.
See the Directory Server documentation for more information: