Howto redirect internet traffic from local machine back to local machine?

[Aseem Rastogi]

also traffic from local machine doesn't pass through PREROUTING chain. 
add this rule to OUTPUT chain of NAT table.

ruben at ruben.cn wrote:

>   REDIRECT
>       This  target  is only valid in the nat table, in the PREROUTING and
>OUTPUT chains, and user-defined chains which are only called from
>those chains.
>       It alters the destination IP address to send the packet to the
>machine itself (locally-generated packets are mapped to the
>127.0.0.1 address).   It
>       takes one option:
>
>       --to-ports port[-port]
>              This  specifies a destination port or range of ports to use:
>without this, the destination port is never altered.  This
>is only valid if the
>              rule also specifies -p tcp or -p udp.
>
>- Ruben
>
>>Hi!
>>
>>Unfortunately i did not find a proper answer on the web although i googled
>>around for quite a lot of time:
>>
>>I want to analyse a malware on my computer. The malware connects to a
>>lot of sites on the internet (hard coded in the program but unfortunately
>>these IPs are encrypted).
>>
>>I know the port the program wants to connect to and i want to answer its
>>requests by a script on the same machine.
>>
>>I tried this for a test to catch connections to mail servers:
>>
>>echo 1 > /proc/sys/net/ipv4/ip_forward
>>iptables -t nat -F
>>iptables -t nat -A PREROUTING -p tcp -d ! 192.168.100.0/24 --dport 25 -j
>>DNAT
>>                --to 127.0.0.1:25
>>
>>But it does not work:
>>
>>$ telnet mail.gmx.net 25
>>Trying 213.165.64.21...
>>Connected to mail.gmx.net.         <--- of course, that's not my box
>>Escape character is '^]'.
>>220 {mp027} GMX Mailservices ESMTP
>>
>>I assume the problem has something to do that the packets are generated
>>on the "iptables-machine". Unfortunately, i only have this machine and
>>thus
>>i cannot send the packets through a second firewall-machine.
>>
>>I would be very happy if any kind soul could give me a hint!
>>
>>Thanks in advance,
>>Martin.
>>
>>
>
>
>
>


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