Implement TCP beacons

[mrcape]

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The goal is to make a shell script or C program that acts as a TCP beacon and on demand forms a client-initiated SSH redirection pipe (kind of a reversed way).
The initial communication is TCP and initiated by the client (behind the firewall), then there is no need to open any ports: the firewall accepts all outgoing traffic.
The beacon is a TCP connection that is initiated in 10 minute intervals. Normally it hangs up after 5 seconds. But if the server responds and sends a specific string into the TCP pipe, the client will try to establish a SSH-connection to server port 22.
Any idea about how to implement the TCP beacons? Thanks.

[Candace]

Packet tagging is a method to mark packets with an internal identifier that can be used as a criterion in the rules for filtering and address translation. With tagging, it is possible to create packages called trust between interfaces and determine if packets were processed by the rules of address translation. It is also possible to do filtering following a policy instead of the filtering rule.