Let’s look at what is an Update Sequence Number (USN)?

The USN, or Update Sequence Number, is the basis of how Active Directory Replication works.

The USN is a value stored with each attribute that changes by either a local change, or a replicated change from a partner domain controller. Each domain controller keeps track of its own changes, and other domain controllers in the infrastructure are aware of all other domain controller USN value.

Active Directory replication relies on Update Sequence Numbers (USNs) on each domain controller. The USN acts as a counter. Each DC’s USN value is unique to a domain controller. The replication system is designed with this restriction in mind. Via 

Launch the below command on the command to know the USN number.

repadmin /showutdvec renjithmenon.local dc=renjithmenon,dc=local