Secondary Active Directory Server

Hi,

I'm running a file server on 10.11.4 and authenticate to AD on Win2012r2.

I have set up a secondary AD server in case the primary one goes down because, well, Windows. But I'm not sure how my file server should automatically find the secondary DC. Do I just add a network DNS address with the backup server's IP to the file server's Network preferences? It looks like I cannot bind to a second AD Server in the Directory Utility, so that's the only way I can see to do it. Am I missing something?

Thanks,

Jeff