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Old 12-15-2012, 01:42 PM   #1
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Loop back IP packets to a NIC?

Hi Folks,

In order to do efficient bidirectional network testing, I would like to return all IP packets incoming to e.g. eth0, i.e. sapping source and destination address of all incomming packets and return them to eth0. Is this possible using iptables and NAT? Of course this can be done for a single port in user space but the gut feeling is that it should be possible and more efficient if done in the same way as conventional NAT.

Old 12-17-2012, 02:30 PM   #2
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Create a loopback cable? Many loopback issues within a nic are not true full nic tests. The nic actually may never get the packet or only into half the nic and then returned to system.
Old 12-19-2012, 10:18 AM   #3
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Well, a loopback cable is not really IP-savy.

I tried:

iptables -t nat -A PREROUTING -p tcp -m tcp -d -j DNAT --to-destination

where is the reflector machine (the one I am issuing the command on) and is the machine to receive the redirected packets, i.e. the sender. However, no success... (to test I telnet and would expect to connect to

Any better ideas or do I miss something?
Old 01-04-2013, 02:17 AM   #4
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IMO you need to do redirect port or call port forward for each program,
eg, telnet run on port 23 and create iptables rules this way

$IPT -t nat -I PREROUTING -p tcp -d --dport 23 -j DNAT --to
$IPT -t nat -I PREROUTING -p tcp -d --dport 23 -j DNAT --to
try it


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