Port 13 TCP -- for use by the Daytime (RFC 867) protocol (Domain Time Server only)
You may also need to specify access permissions based on username. See KB1001.034 for details.
If you are restricting access by machine IP number as well, then only Domain Time's designated
Time Server (by default the domain's PDC) needs access to these ports. Other machines in the
domain will retrieve the time from the Time Server directly, and do not need Internet access.
There are no known security risks associated with opening these ports.
The protocols are fairly simple, and cannot be used to gain control of
or access to your protected machines.
IMPORTANT: See the Planning page of the Domain Time II Documentation for more detailed discussion of network requirements.