CMS Extensions - firewall

The moodle 2 plugin running on one server is failing to connect ("Unable to login"... error on local plugin config page) to the kaltura server. Both are physical and different servers and can ping each other, firewall is switched off on the kaltura server as our network firewall is sufficiently heavyweight. Both servers are in our main DMZ.

As a test, I installed it on my localhost moodle2 which is on our internal pc network. This can access kaltura via the plugin just fine, and with the right uID settings for player etc in let me upload and play a video which shows in the Publisher console.

I setup a test PHP script which runs fsockopen() to port 80 on it, and retrieves a custom php page which just returns Hello world (boring but functional). This occasionally gives me a "connection actively refused (10061)" error but most of the time works. Should the plugin be doing anything other than port 80 traffic?

Thanks,
Dave