Order of rules when NAT'ing.

[Scotty Gammenthaler]

> Hi! 
>
> Question following might be considered stupid, but here goes: 
>
> When making up a POSTROUTING NAT table, is the order of the rules vital? 
>
> Example: 
>
> iptables -t nat -A POSTROUTING -s 192.168.2.0/24 -o eth0 -j SNAT --to 
> 4.3.2.1 
> iptables -t nat -A POSTROUTING -s 192.168.2.10 -o eth0 -d 1.2.3.4 -j 
> SNAT --to 5.6.7.8 
>
> In the case above, what will packages going from 192.168.2.10 to 1.2.3.4 
> end up beeing SNAT'ed to? 
>
> Thanks in advance! 
>
> Regards 
> Sture Lygren 

I'm no expert on this, but according to the Linux 2.4 NAT HOWTO
(see http://www.samba.org/netfilter/unreliable-guides/NAT-HOWTO.html, 
Section 5), "...each rule is examined in order until one matches."

So the order is vital and I would expect your packet to match the 
first rule and get SNAT'ed to 4.3.2.1.

Scotty Gammenthaler

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