Skype hosts list
So, in many circumstances where UTM-device are not available, the best approach is to deny all traffic to Skype hosts. So, what are the IP addresses used to authenticate? The hosts I found are included in the following networks:
- 111.221.74.0/24
- 111.221.77.0/24
- 157.55.130.0/24
- 157.55.235.0/24
- 157.55.56.0/24
- 157.56.52.0/24
- 194.165.188.0/24
- 195.46.253.0/24
- 213.199.179.0/24
- 63.245.217.0/24
- 64.4.23.0/24
- 65.55.223.0/24
Please note that, while I masked all network with a C subnet (/24), the real subnet mask can be quite different (ie: it can be a smaller /28 netmask). However, any false positive should be easily detectable by simply enabling connections logging on your firewall.
For a complete connections log of my Skype login attempt, you can download this file.
A blocked Skype login attempt
Sure, a new Skype version and/or upgrade can boast a new hosts list, but this approach should work in a number of cases: I tested both Skype beta 2.2 for Linux and Skype 5.9 for Windows XP, and both were blocked by my gateway firewall.