Can't Test Authentication Against AD on Windows Server 2012 R2

I have an Windows Server 2012 R2 Domain Controller that I’d like to authenticate my users against. This machine sits on our LAN behind a firewall. I have control of the firewall (it’s a Cisco PIX 506e).

When I enter all the parameters in the settings page and try to do a test, it fails. On the firewall I’ve added a line on my inbound ACL to allow TCP and UDP traffic to port 389 (see below)

access-list inbound line 4 permit tcp any interface outside eq ldap (hitcnt=4)
access-list inbound line 5 permit udp any interface outside eq 389 (hitcnt=0)

As you can tell by the hit count, it looks like the TCP traffic is reaching the firewall. So I added a static statement to forward those packets to my DC (see below):

static (inside,outside) tcp interface ldap 172.23.6.127 ldap netmask 255.255.255.255 0 0

At this point I’m not sure what else I can do. Traffic seems to be getting to the firewall and then being forwarded to the DC. Any help would be appreciated, thanks.

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