Your network contains an Active Directory domain. The functional level of the domain is Windows Server 2003. The domain contains five domain controllers that run Windows Server 2008 and five  domain controllers that run Windows Server 2008 R2.  
You need to ensure that SYSVOL is replicated by using Distributed File System Replication  （DFSR）. 
What should you do first（）

Your network contains a single Active Directory domain that has two sites named Site1 and Site2.  Site1 has two domain controllers named DC1 and DC2. Site2 has two domain controllers named  DC3 and DC4.  DC3 fails.  
You discover that replication no longer occurs between the sites. You verify the connectivity  between DC4 and the domain controllers in Site1.  On DC4， you run repadmin.exe /kcc.    
Replication between the sites continues to fail.  
You need to ensure that Active Directory data replicates between the sites.    
What should you do（）