How can I verify AD replication between two DCs works

We have a domain with 3 DCs in different networks and we want to decomission one of them.

However, I suspect that the two remaining DCs will not replicate properly between each other due to some network misconfiguration. So I want to ensure that, after I switch off the obsolete DC, the two remaining ones will replicate flawlessly between each other.

I can ping between the two DCs without any problems, but I suspect replication might be a different story.

When I issue repadmin /showrepl dc1, it will only show the status of the previous replications with the DC I want to remove. The safe DC is not listed.

Solution 1:

Have you tried DCDIAG? It has lots of tests including Checks for timely replication and any replication errors between domain controllers

Here is a link to Dcdiag information:

https://technet.microsoft.com/en-us/library/cc731968(v=ws.11).aspx

Solution 2:

To ensure two DCs replicate with each other, you can follow the guide Forcing Replication.

You first want to ensure that both clean DCs replicate with each other.

1. Open Active Directory Sites and Services, navigate to your first DC and open the NTDS Settings.

2. You will probably see a connection to the old DC. Add a new connection for the new DC. Now force replication with your other DC.

   

   Repeat the process for the other DC.

3. Now inspect replication results for your DCs:

   repadmin /showrepl dc1
   

Solution 3:

You can also use the graphical utility MS has and checks all AD Forest for replication issues.

https://www.microsoft.com/en-us/download/details.aspx?id=30005

Thank you