How to avoid port scanners

[Eduardo Gonçalves <egsilva@prolan.com.br>]

Hi all,

I have a ipchains rule like this:
#ipchais -A input -s 0/0 -p tcp -y -j REJECT

so I can block all the SYN packets used by port scanners and avoid them...
but now I run a smtp server (postfix), and my box must accept SYN packets to
port 25.

I don't want that anybody knows ( using a scanner ) which is the open port.

My question:
How can I block port scanners(like nmap) and run my server without
problems?


thanks a lot
[]'s
Eduardo
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