When synchronizing data between two Active Directory domains, Synchronization Service uses the following ports to access domain controllers in the domains:
| 
 Port  | 
 Protocol  | 
 Type of traffic  | 
 Direction of traffic  | 
| 
 53  | 
 TCP/UDP  | 
 DNS  | 
 Inbound  | 
| 
 88  | 
 TCP/UDP  | 
 Kerberos  | 
 Outbound  | 
| 
 389  | 
 TCP/UDP  | 
 LDAP  | 
 Outbound  | 
| 
 636  | 
 TCP  | 
 LDAP over SSL (LDAPS)  | 
 Outbound  |