Re: ip_local_deliver related query

[Patrick McHardy <kaber@trash.net>]

Vasantha Kumar Puttappa wrote:
> Hi,
> 
> ( I am assuming packet arrival to the local host)
> 
>   As far as I know Netfilter hook  for "INPUT" chain is called just before
> the ip_local_deliver() function is called. If I am not wrong,
> ip_local_deliver function will remove the IP header and gives the packet
> to appropriate function in transport layer ( TCP or UDP or ICMP
> Process).
> 
> 
>  What I am want to do is to change the source IP address of the IP packet
> just before calling the ip_local_deliver() using IPtables.
> 
> So I want know, will this go smoothly assuming there is a socket waiting
> for this kind of packet(packet with new source IP address) or will
> something go wrong ?

This is exactly what NAT does. If you use DNAT in LOCAL_OUT, a SNAT
mapping is also set up for LOCAL_IN. The socket lookup is performed
later in the individual protocols, so it will use the rewritten
source address.