iptables: drop or reject?

[Bill Davidsen]

Ashley M. Kirchner wrote:
> 
>    To drop or not to drop, that is the question.  If there's a server 
> out there sending spam e-mail, and I use iptables to block it, is it 
> best to simply drop the packet, or should I do a '--reject-with 
> icmp-host-unreachable' (or 'icmp-port-unreachable') or just a 'tcp-reset'?
> 
>    Basically, if I just drop the packet, the server in question would 
> simply continue to send stuff, wouldn't it?  As far as it knows, its 
> spam reached the destination, whereas if I send something back, it might 
> actually acknowledge and stop?  Yes?  No?
> 
If you drop, the sending host will often keep sending SYN packets until 
it decides you are talking, maybe 3-10 packets. If you send back an 
unreachable status it may not try again until later. I also played with 
the port-administratively-prohibited status, and a "TOS-host-redirect" 
packet suggesting the best route to the network was 127.0.0.1. ;-)

I'd reject, in general it will reduce the number of packets you get.

-- 
Bill Davidsen <davidsen at tmr.com>
   "We have more to fear from the bungling of the incompetent than from
the machinations of the wicked."  - from Slashdot