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From: securitylists () uniontown com
Date: Thu, 27 Dec 2007 13:35:05 -0500 (EST)
What you are describing sounds like "port knocking". Sorry, no links, but Google will certainly help you if you use
Ong Chin Kiat wrote ..
I've recently used an SSH server that had an interesting authentication
mechanism. You first had to telnet to the machine on a certain port.
After doing this (it will just time out - no prompt), you then SSH to
the server in question. The telnet step has to be carried out, if not
SSH will just time out.
My question is, is this called reflexive firewalling, and can I
duplicate this with iptables?