Check Replication Status of Domain/Forest

Source: https://technet.microsoft.com/en-us/library/dd464018(WS.10).aspx

"Run the following Repadmin.exe command to ensure that replication is working throughout the forest:

repadmin /replsum /bysrc /bydest /sort:delta

All domain controllers should show 0 in the Fails column, and the largest deltas (which indicate the time that has elapsed since the last successful replication) should be less than or roughly equal to the replication frequency of the site link that the domain controller uses for replication. The default replication frequency is 180 minutes."