Page contains a FAQ on u.select external interfaces.

What u.select server do I need to create a firewall exception for, so the external interface works?

An external interface can only work when u.select is allowed to establish connections to your interface via its defined URL. Since u.select is comprised of multiple u.select servers, you must create a firewall exception for your school's home u.select test server and home u.select production server.

Here are the u.select test and production IP addresses and URLs: