I've been doing some research on creating covert channels using icmp packets and a bounce server and so far everything worked fine. I can contact my web server through a bounce server outside of my network (like www.google.com or whatever). In my current setup both client and target are located in the same network and comunicate through the bounce server using icmp packets.
Speaking of covert channels... http://www.cs.tau.ac.il/tausec/lectures/Network_Covert_Channels.pps
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