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Article #192

Re: IPTables forwarding rule

#192
From: Harry Phillips
Date: Sun, 25 Jul 2004 08:44
36 lines
2377 bytes
caliban@rootshell.be wrote:
>>
>>Do I use the NAT and PREROUTING, POSTROUTING, FORWARD? I have examples 
>>from the Internet if the Linux box and the host it is forwarding to are 
>>on different networks but not when they are on the same network.
> 
> 
> I assume you tried DNAT on the PREROUTING chain?
> The problem is probably with routing --
> your packets from ADSL modem are going to the linux box and
> having their destination IP rewritten as .1.50 but the source IP
> remains
> ADSL so when the .1.50 box replies to these it will send the packets
> to ADSL and thus the default router (.1.254) knowing nothing of this
> connection drops them.
> 
> The trick is to both DNAT on the PREROUTING chain and SNAT on the
> POSTROUTING chain (twice nat?)
> eg
> $IT -t nat -A PREROUTING -j DNAT -p tcp -s $ADSL -d $ALIAS --dport
> $PORT --to-destination=192.168.1.50:$PORT
> 
> $IT -t nat -A POSTROUTING -j SNAT -p tcp -s $ADSL -d 192.168.1.50
> --dport $PORT
> --to-source=$ALIAS
> 
> 
> Where ALIAS is an IP alias for your linux box and ADSL is your modem
> IP.

Thanks you very much I have tried this and it works exactly they way I 
want it to.

-- 
Regards,
Harry Phillips
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Date: Sun, 25 Jul 2004 18:44:01 +1000