Re: [RFC PATCH] netfilter: nf_nat: support user-specified SNAT rules in LOCAL_IN

[Patrick McHardy <kaber@trash.net>]

Jan Engelhardt wrote:
> On Wednesday 2010-06-16 17:09, Patrick McHardy wrote:
>   
>>    
>>    This works well, but is needlessly complicated for cases where only
>>    a single SNAT/DNAT mapping needs to be applied to these packets. In that
>>    case, all that needs to be done is to assign each network to a seperate
>>    zone and perform NAT as usual. However this doesn't work for packets
>>    destined for the machine performing NAT itself since its corrently not
>>    possible to configure SNAT mappings for the LOCAL_IN chain.
>>    
>>    Example usage with two identical networks (192.168.0.0/24) on eth0/eth1:
>>    
>>    # assign packets from each interface to a seperate zone and mark them for NAT
>>    
>>    iptables -t raw -A PREROUTING -i eth0 -j CT --zone 1
>>    iptables -t raw -A PREROUTING -i eth0 -j MARK --set-mark 1
>>    iptables -t raw -A PREROUTING -i eth1 -j CT --zone 2
>>    iptabels -t raw -A PREROUTING -i eth1 -j MARK --set-mark 2
>>    
>>    # SNAT packets to private networks: eth0 -> 10.0.0.0/24, eth1 -> 10.0.1.0/24
>>    
>>    iptables -t nat -A INPUT       -m mark --mark 1 -j NETMAP --to 10.0.0.0/24
>>    iptables -t nat -A POSTROUTING -m mark --mark 1 -j NETMAP --to 10.0.0.0/24
>>    iptables -t nat -A INPUT       -m mark --mark 2 -j NETMAP --to 10.0.1.0/24
>>    iptables -t nat -A POSTROUTING -m mark --mark 2 -j NETMAP --to 10.0.1.0/24
>>     
>
> I am not sure I follow whatever this is supposed to do.
>
> Packet from eth0: src=10.0.0.15 dst=10.0.1.22
> INPUT#NETMAP will dst transform that to dst=10.0.0.22

nat/INPUT performs source NAT, not destination NAT.

> POSTROUTING#NETMAP will src transform that to src=10.0.0.15
>
> Is is this step that makes no sense to me.

Does it make sense now?