To start off, I am *not* advocating this. Am highlighting it more from a security perspective (as a hole and how it is exploited) rather than anything else.
Suppose you are at a hotel or an airport and you have a paid-browsing service.
Is it possible that someone can leech off your system?
Yes. It is possible to do IP over DNS and / or ICMP, if all you do is simple firewalling.
First, some defs:
IP - Internet Protocol - which is the foundation for most the web
DNS - is Domain Name System - this is the box that converts names to IPs and vice versa, ie. Its responsible for the "www" dogma.
ICMP - Internet Control Message Protocol
What do i need?
"ingredients" - a domain, a public ip and control of a dns, that's it!
How
Here's a tutorial on DNSTX and ICMPTX which details the configuration over DNS and ICMP, respectively.
Apparently, if UDP is open on port 53, one can even OpenVPN on it.
Awareness / tracking:
Use a packet filter, which support connection tracking - like PF.
Will do a follow-up post on how can one defend against it.
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