IWSS functions both as an antimalware and content filtering web application and users want to know if it is possible for IWSS to block or prevent Skype from making a call.
IWSS cannot block a Skype connection because Skype does not use pure HTTP/HTTPS to connect. IWSS can only handle or block HTTP/S and FTP traffic so it will not block any of the ports and services that Skype uses for connection.
In order to block Skype, you will need to combine a gateway content filtering and firewall application or device.
To discuss this further, Skype uses supernodes with a range of ports when performing a VOIP call.
- Skype will attempt to contact supernodes. The IPs of these supernodes are in a file stored with other files that Skype installed.
- The source ports that Skype attempts to connect from are non-default ports.
- Once the connection is establish, the rest of the communications are done in TCP over non-default source ports with the range 2940-3000.
- If the above failed, only then will Skype use the proxy server (IWSS in this case) specified in Internet Explorer and attempt to tunnel the traffic over port 443 using the SSL protocol.
- The destination IPs are random as above, which makes destination blocking out of the question.
- An option will be to block SSL connections, but this will affect all other connections going through SSL.