As seen in the previous Figure, the Directory Server assigns a unique change number to each update operation (specifically, ADD, DELETE, MODIFY, or MODIFY DN operations) to track each request when received from a client. The change number not only identifies each and every update, but it also allows ordering updates to the replicated data the same way on each Directory Server. The change number is composed of the following multiple fields:
  • Timestamp that identifies when the update was made. The timestamp is time-zone-independent and recorded with millisecond resolution.
  • Server ID that uniquely identifies the Directory Server where the update was made.
  • Sequence number that defines the order of the updates received from external clients at a particular directory server.

The replication protocol also sets a virtual clock that eliminates the need for synchronized time on servers. For troubleshooting purposes, however, it is still recommended to keep the system clocks synchronized.