Block Skype connections

There is a popular belief that Skype client is very hard to block on the network layer, due to it’s Peer-To-Peer behavior and usage of HTTP/S ports.

Block Skype client

However at present time (December, 2012) Skype client connections can be blocked pretty simply by a few firewall rules.
After startup, Skype client receives a number of it’s master (login?) servers – Currently there are 16 DNS entries from to

Using simple bash script (uses Linux DNS utility – dig) we can get most of these server’s IP addresses:

for i in {0..20} ; do dig +short dsn$; done | sort | uniq

Just block all access to following networks and Skype client won’t be able to authenticate and connect.

For Linux router, with IPtables firewall, you may use following command:

for ip in; do iptables -A OUTPUT -d $ip -j DROP; done