TRL,
LOGOS runs in UDP2343 port and when the connection with a client is established opens a second UDP port (dynamically assigned by OS) between 1024 and 65535.
Therefore, you can not know previously what port is going to be opened. However, there is not a major risk on keeping those ports open since you probably don't have any harmful applications listening on the UDP ports greater than 1023.
For further information, search for "Networking Lookout or the LabVIEW DSC Module Across Firewalls" (http://zone.ni.com/devzone/conceptd.nsf/webmain/7D0E7F20B1A7C8E486256A39005747F2?opendocument)
Even though this link is for Labview, it may be useful since Labview uses Logos too.(http://digital.ni.com/public.nsf/3efedde4322fef19862567740067f3cc/f0de7a1a88d92d6d86256d710
049fb40?OpenDocument)
Good luck
JSS