Introduction

In most situations you are going to have VPN or private network to allow DC to DC traffic to work across the internet, in fact you would need either a VPN or private link as NAT would not allow it to work period. In the rare cases you would need to allow the communication between non-natting internal firewalls on different networks. This is what you'd need to allow

Required Ports

 ICMP 8
 ICMP 0
 TCP/UDP 389
 TCP 636
 TCP 3268
 TCP 3269
 TCP/UDP 88
 TCP/UDP 53
 TCP/UDP 445
 TCP 25
 TCP/UDP 135
 TCP/UDP 49152 - 65535
 TCP 5722
 TCP/UDP 464
 TCP 9389
 TCP 139
 UDP 123
 UDP 137
 UDP 138

I know there is a lot of ports required. Especially the large range of ephemeral ports. This is because Windows uses a port mapper to map these ephemeral ports. You can download the handy port query tool from Microsoft for finding out which ports are in use: PortQryUI – GUI – Version http://www.microsoft.com/download/en/details.aspx?id=24009 or google it of course. Thanks to Ace Fekay for his post: http://blogs.msmvps.com/acefekay/2011/11/01/active-directory-firewall-ports-let-s-try-to-make-this-simple/