Re: Duplicate IP scenario. Doable with iptables?

["John A. Sullivan III" <john.sullivan@nexusmgmt.com>]

On Tue, 2004-11-23 at 14:44, Kevin Hilscher wrote:
> I have a somewhat odd scenario that requires the same pools of 192.168
> IPs to be bound to eth1 and eth2 on the same machine. I need to NAT
> another pool of 10.x.x.x IPs bound to eth0 to these two pools of 192.168
> IPs. The setup is as follows:
>  
> eth0:10.115.0.1/16 -> eth1:192.168.0.1/24
> eth0:10.115.0.2/16 -> eth1:192.168.0.2/24
> eth0:10.115.0.3/16 -> eth1:192.168.0.3/24
> eth0:10.115.0.4/16 -> eth1:192.168.0.4/24
> eth0:10.115.0.5/16 -> eth1:192.168.0.5/24
> eth0:10.115.0.6/16 -> eth1:192.168.0.6/24
>    
> eth0:10.116.0.1/16 -> eth2:192.168.0.1/24
> eth0:10.116.0.2/16 -> eth2:192.168.0.2/24
> eth0:10.116.0.3/16 -> eth2:192.168.0.3/24
> eth0:10.116.0.4/16 -> eth2:192.168.0.4/24
> eth0:10.116.0.5/16 -> eth2:192.168.0.5/24
> eth0:10.116.0.6/16 -> eth2:192.168.0.6/24
>  
> Suse 8.1 has no problem letting me bind the same IPs to eth1 and eth2,
> since eth1 and eth2 are not on the same physical network. However, I am
> having problems writing my NAT rules for this scenario.
>  
> Is this scenario doable under iptables?
>  
> TIA,
>  
> Kevin
Hmmm . . . that's an interesting one.  Let's break it into SNAT and
DNAT.  I think you will be able to keep the packets straight in DNAT by
specifying the inbound interface, e.g., 
iptables -t nat -A PREROUTING -i eth2 -d 192.168.0.1/24 -j DNAT
--to-destination 10.116.0.1

On SNAT, we can keep the packets straight based upon source, e.g., 
iptables -t nat -A POSTROUTING -s 10.116.0.6 -j SNAT --to-source
192.168.0.6

but I'm not sure how one makes sure the packet goes out eth2 rather than
eth1.  I think the interface decision has already been made but I'm not
sure.  If it has been, I wonder if one could use policy routing in
iproute2 to make it work.  One could set up a rule to route to an
interface based upon source.  It might be worth a try.  Good luck - John
-- 
John A. Sullivan III
Chief Technology Officer
Nexus Management
+1 207-985-7880
john.sullivan@nexusmgmt.com
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