how to change ip source address of incoming packets

Gáspár Lajos swifty at freemail.hu
Wed Nov 15 09:13:07 CET 2006



Matevz Langus írta:
> Does anyone know how to change ip source address when entering Linux 
> interface to something else and when leaving out the same interface 
> (backwards) changing it back.
>
> The problem is this:
>
> I have 10 devices with the same IP address, 192.168.1.1. They are 
> connected to ethernet switch, which adds VLAN TAG to packets from each 
> device. Linux box is connected to the switch. It is possible to create 
> 10 VLAN interfaces on the Linux box and only one 192.168.1.1 address 
> will be seen per interface. In order to establish TCP connections to 
> all devices at the same time, source address must be altered.
>
> on eth0.10, INPUT SRC 192.168.1.1 -> 192.168.10.1
> on eth0.10, OUTPUT DST 192.168.10.1 -> 192.168.1.1
> on eth0.11, INPUT SRC 192.168.1.1 -> 192.168.11.1
> on eth0.11, OUTPUT DST 192.168.11.1 -> 192.168.1.1
> ...
>
Try this :

iptables -t nat -A POSTROUTING -j SNAT -i eth0.10 -s 192.168.1.1 
--to-source 192.168.10.1
iptables -t nat -A PREROUTING -j DNAT -o eth0.10 -d 192.168.10.1 
--to-destination 192.168.1.1
> thanks,
>   Matevz Langus
>
>
Swifty




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