The URL where your catalog is located. Do not include anything after the hostname.

Correct: http://addison.vt.edu http://addison.vt.edu:83 http://addison.vt.edu:8991

Incorrect:
addison.vt.edu
http://addison.vt.edu/
http://addison.vt.edu/F
http://addison.vt.edu:83/F