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

[Patrick McHardy <kaber@trash.net>]

Jan Engelhardt wrote:
> On Thursday 2010-06-17 09:44, Patrick McHardy wrote:
>   
>> Jan Engelhardt wrote:
>>     
>>> 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?
>>     
>
> Somewhat, but there's still
>
>   
>>>> However this doesn't work for packets  destined for the
>>>> machine performing NAT itself
>>>>         
>
> Why would it not? What would cause misdelivery if PREROUTING
> was used instead of INPUT?
>   

PREROUTING performs DNAT. The purpose is to map the two
identical networks to non-clashing networks. Just consider two
connections from the same source address and port number
to the same destination.