How to route the traffic from machine 1 to machine 3 via machine 2 and vice versa, on the same subnet?

Question

I've a Citrix Xenserver where I'm running VMs. I have three VMs there, and they have 2 NICs each: eth0 is my company LAN which I'm using for management, and eth1 is a "single-server private network" on all three VMs. The management interface is just for my SSH sessions.

The IPs assigned to my VMs are:

M1 = 192.168.0.1/24
M2 = 192.168.0.2/24
M3 = 192.168.0.3/24

On M2, I've got IP forwarding enabled:

echo 1 > /proc/sys/net/ipv4/ip_forward

To route the traffic via M2 from M1 to M3:

ip route add 192.168.0.3 via 192.168.0.2 dev eth1

Likewise on M3:

ip route add 192.168.0.1 via 192.168.0.2 dev eth1

But when I traceroute or send traffic from M1 to M3 (or vice versa), it seems to be going straight to the destination instead of going through M2. Is it because they are on the same subnet? If they are on the same subnet, what should be done on my Linux machine to achieve this routing?

Answer 1

Networks:

1. Create a single-server private network on Xen.
2. Add it machine1 and machine3, one each.
3. Add two of them created at step 1 to machine2.

Machine1:

ip addr add 1.1.1.2/24 dev eth1
ip route add 2.2.2.0/24 via 1.1.1.1 dev eth1 proto static

Machine3:

ip addr add 2.2.2.2/24 dev eth1
ip route add 1.1.1.0/24 via 2.2.2.1 dev eth1 proto static

Machine2 (router):

ip addr add 1.1.1.1/24 dev eth1
ip addr add 2.2.2.1/24 dev eth2

Testing:

ping 2.2.2.2 # machine1
ping 1.1.1.2 # machine3