RE: Reflexive firewalls?

[krymson () gmail com]

Yes! The previous Google mentions by others will give you good results, as port knocking (triggering) has been 
available for iptables for many years.  Or just go here: http://www.portknocking.org/

You can also call it "single packet authorization" which is something fwknop will do for you, in combination with 
iptables.

http://www.cipherdyne.org/fwknop/


<- snip ->
> 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?