Computer Configuration > Policies > Centrify Settings > Mac OS X Settings > Firewall > Enable iChat
On Mac OS X Servers, enabling this policy has no effect. If the firewall is enabled, the iChat service is not allowed through the firewall.
If the firewall is enabled, enabling this group policy is the same as clicking the On checkbox to allow communication through the firewall for iChat Bonjour. If you do not enable this group policy, traffic for iChat Bonjour will be blocked from the local computer.
This policy can take effect dynamically at the next group policy refresh interval without rebooting the computer.