Thanks micheal,
The server is given to me by one of my supervisors, so i looked on the internet for a way to know if the server is registred with redhat and i found this command :
sudo subscription-manager status
and this was the reponse of the server :
+-------------------------------------------+
System Status Details
+-------------------------------------------+
Overall Status: Unknown
And i think that the server is not using any proxy since i can ping to
www.google.com