Re: Iptables SNAT for pkt generated by internal process

[Alexandru Dragoi <alex@zoomnet.ro>]

moniacheli@tiscali.it wrote:

>I would like to use iptables to translate the source of IP datagrams 
>generated inside a router for some particular applications (such as 
>syslog: protocol UDP, destination port 514). I thought to use an 
>iptables rule defined by an OUTPUT chain (which let manipulate datagram 
>generated from local process) and by the target SNAT (which let to 
>translate ip source) -> iptables -t nat -A OUTPUT -p udp --dport 514 -j 
>SNAT --to x.x.x.x. The problem is that the OUTPUT chain cannot be used 
>with the target SNAT!
>Has anybody any idea about which is the best and simplest way to get 
>the result described above?
>
>Thanks for Your collaboration.
>Monia Cheli
>
>
>
>
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You do SNAT in POSTROUTING. Local generated packets also enter
POSTROUTING. You may want to match source ip or .. you can mark packets
in mangle OUTPUT, and then SNAT in POSTROUTING matching only the mark
value with mark match.