LDAP query to port 389 failed

Hi all,

I have a total of 3 DC in my environment. Replication from DC1(Server 2003) to DC2(Server 2003) no problem. But from DC1 to DC3(Server 2008 r2) i am facing some problem.

I did some network test using portqry(DC1 to DC3) and found out that this port UDP 389 is not working on DC3.

Error msg: LDAP query to port 389 failed. Server did not respond to LDAP query.

My network engineer has confirm that no firewall rules is blocking this port. Windows firewall is also disable.

Other ports that is relevant to AD replication is working fine.

I also did a portqry locally on DC3 and got a successful LDAP response.

May i know what other possibility can cause this port to fail?

Thanks you