The ports that Skype (version 6.11) uses are 443 and 80 by default. These ports are also used by other programs like IIS, XAMPP etc. Some times you may need to change the port that skype uses to some other port.
You can change the ports that Skype uses by first launching SKYPE,
Click Tools and then Options.... Now you see the defaults when you click Advanced and followed by clicking Connection as shown.
Uncheck the check box and choose a different port. The new ports will become acctive when you start SKYPE next time. I had to quit the program and login again to display the changed conditions.