Re: Could someone tell me the rules of port translation in SNAT ?

["ding dang" <jiadeip@hotmail.com>]

> > When using SNAT of Netfilter as an NAPT, how will Netfilter assign the
> > public UDP port for a UDP request from the private network to Internet?
>
>With both TCP and UDP, netfilter will use the source port contained in the
>original packet if it can (ie: if that source port is not being used for
>something else by the netfilter machine).   If this is not possible, then
>another port is chosen at random using the standard socket-binding 
mechanism
>used for any network connection.
>
> > Could someone detail it to me when the UDP request is
> > NEW/ESTABLISHED/RELATED/REPLIED/UNREPLIED?
>
>This makes no difference.

Thanks.

But what i observed is:(SNAT using UDP port 20000-30000)

private addr         netfilter port         Internet addr
10.0.0.8:2000 --->       20000       ---->   193.0.0.8:3000
10.0.0.8:2001 --->       20000       ---->   193.0.0.8:3001
10.0.0.8:2002 --->       20000       ---->   193.0.0.8:3002
that means DIFFERENT UDP requests from private network for DIFFERENT 
Internet destination result in a same Netfilter port no matter the Internet 
destination sends reply or not ;

private addr         netfilter port         Internet addr
10.0.0.8:2000 --->       20000       ---->   193.0.0.8:3000
10.0.0.8:2001 --->       20001       ---->   193.0.0.8:3000
10.0.0.8:2002 --->       20002       ---->   193.0.0.8:3000
DIFFERENT UDP requests from private network for a SAME Internet destination 
result in DIFFERENT Netfilter ports, why?

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