Packets go to the wrong interface (no source address checking?)

[Sjors Gielen <mailinglist@dazjorz.com>]

Hey all,

I'm trying to set up a virtual machine with two IP's in a virtual 
network. This virtual network is created by the program 'hamachi', a 
zeroconfig VPN program which creates an interface using tun, sets a 
dedicated IP and tunnels everything through this interface to everyone 
else in the same Hamachi network.

So I wanted two IP's in the machine; I have Hamachi running two times 
and I have two interfaces now, ham0 and ham1. There are also two routes:

Destination   Gateway  Genmask    Flags  Metric  Ref  Use  Iface
5.0.0.0       *        255.0.0.0  U      0       0      0  ham0
5.0.0.0       *        255.0.0.0  U      0       0      0  ham1

When I ping the ham0 IP, I get a response, everything is OK. However, 
when I ping ham1, I get no response. I think this is because the kernel 
wants to reply to me, 5.187.x.y, and sees the first route for ham0 in 
the route list; but then the driver (or tun/tap) sees the source address 
is wrong and refuses to send the packet.

Is this diagnosis true? How would I solve something like this? Anything 
else needed to diagnose this? Any help is appreciated.

I'm not sure if this is the right list to send to, please correct me if 
it isn't.

Thanks,
Sjors