How to verify successful replication of two domain controllers

When you do a Burflags D2 recovery, the upstream it uses must be healthy. If both DCs are in error state, doing D2 on one will not help. I assume you only have 2 DCs.

You might have to use the D4 on one and D2 on all other DCs in domain. If ging down this road

1. Stop FRS on all
2. Set D4 on one and start it.
3. Wait until it has initialised and has completed (you will see netlogon and sysvol share on that DC when you do "net share" locally)
4. Do D2 on one DC at a time and start FRS

For more details, please see the KB 290762 mentioned in above blog article.

If you end up haveing to troubleshoot upstream as well, you might end up using FRSDiag. Details are at http://blogs.technet.com/b/askds/archive/2008/05/30/how-to-get-the-most-from-your-frsdiag.aspx

I also want to recommend that you monitor the SYSVOL replication state using free tools like Ultrasound so you can proactively resolve issues (before realising at GPO editing time). Latest version is at http://blogs.technet.com/b/askds/archive/2008/09/10/ultrasound-released-for-windows-server-2008-and-sql-server-2005.aspx

While knowing how to do this can be useful in certain situations, as EEAA pointed out, you should probably have two DCs instead of one. If for nothing more than a disaster recovery/ backup.

If you are not performing backups of your current DC... START PERFORMING AD BACKUPS BEFORE DOING ANYTHING ELSE.

You should be able to do this without too much headache. After making the change you should definitely make it a priority to document where references to your DCs are in your environment.

This should be done at a time to minimize downtime.

1. Bring up your new DC using a new static IP address. Have it DCPromo'ed in and make sure it's fully functional before proceeding. (Have the new DC point to the original for DNS)
2. Give the 2008R2 DC the new static address, and the 2012R2 DC the original IP.
   3. Client side DNS Settings on the DCs here are important, if you are keeping two DCs DNS should point to the opposite DC then itself. If you are only keeping the one, point DNS to itself on both.
3. Restart AD DS services on both DCs, as well as the netlogon service.
4. Check DNS to ensure that all the records have been updated appropriately (A, & SRV)
5. Check AD logs to ensure there are no issues with replication (either FRS or DFSR)

If you were going to remove the original DC, you would then:

1. Transfer any FSMO roles the DC holds
2. DCpromo the DC out
3. Verify it has been demoted properly and all SRV records have been removed from DNS.

If you still need a temporary fix for applications that point to a removed DC by name, you could add a CNAME record to DNS for that DC that points to the new DC.

Again, you should probably have two DCs.

Also, for further insight and information, see this other SF question: Windows 2003 DC to Windows 2008 R2 DC with same name and same IP that takes into account other factors that might be involved (same concepts apply in your situation still).