Re: When do the rule apply?

[Andy Smith <andy@strugglers.net>]

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On Wed, Jun 15, 2005 at 10:01:54PM +0200, Alexander Salmin wrote:
> Hi, I guess this question is just a silly one for experts, but I can't
> find the answer anywhere so I'm asking you guys.
> 
> In what order do the assigned rules apply in this script? 
> 
> # Example1
> iptables -A INPUT -j DROP # rule #1
> iptables -A INPUT --dport 80 -j ACCEPT # rule #2
> 
> #Example2 
> iptables -A INPUT --dport 80 -j ACCEPT # rule1
> iptables -A INPUT -j DROP # rule2

They apply in the order you've issued them since they are operating
on INPUT and they are appending.

> Will the both examples produce the same result?

No; example1 drops everything to INPUT with rule 2 never being
reached, but example2 would ACCEPT packets to port 80.. although
wouldn't that be a syntax error without at least -p tcp or -p udp to
tell it that it is something that has ports?

> Or will rule2 in example 2 make rule1 in example2 vanish because it's
> telling the system to drop all?

No, rules don't affect other rules.  They may not be reached however.

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