Re: Redirecting traffic from a non-existent IP

[Pascal Hambourg <pascal.mail@plouf.fr.eu.org>]

Hello,

Julian Hagenauer a écrit :
> Hi,
> i am running Linux 2.6.11.12-xen0 (binary distribution).
> I want to route all Traffic destined to 192.168.1.5 to 192.168.1.3.
> 192.168.1.5 is a non-existent IP/host, 192.168.1.3 is a Xen-VM running 
> on localhost, so 192.168.1.5 should act as a kind of alias for 
> 192.168.1.3 and be accessible from localhost.
[...]
> iptables -t nat -A PREROUTING -d $MAP_FROM -j DNAT --to $MAP_TO
> echo "Aktuelle Nat-Regeln:"
> iptables -t nat -L
> 
> But ping 192.168.1.5 or ssh 192.168.1.5 still does not work.
> I have no clue what's wrong.

I guess the problem is ARP. If nothing replies to the ARP requests for 
192.168.1.5 sent by th host which want to send a packet to this address, 
then IP packets for this destination aren't even sent (that should 
produce Host Unreachable error messages).

Possible workarounds :
- set up some ARP daemon on the network that will reply for 192.168.1.3
- set a static ARP entry in the senders' ARP table (heavy)
- set a static route to 192.168.1.5 with gateway 192.168.1.3 (I know, 
that's ugly)
- maybe it is possible to use arptables on the NAT box to make it reply 
to the ARP requests (I don't know anything about this)

I guess IP aliasing is not an option.