I have a machine called A with IP address 192.168.1.1/netmask 255.255.255.0

Another machine B with 192.168.1.2/netmask 255.255.255.0

There is no gateway entry specified in routing.
Their routing table is
For A
Destination Gateway Genmask Flags Metric Ref Use Iface
192.168.1.0 0.0.0.0 255.255.255.0 U 0 0 0 eth0
For B
Destination Gateway Genmask Flags Metric Ref Use Iface
192.168.1.0 0.0.0.0 255.255.255.0 U 0 0 0 eth0


Now I am able to ping A to B as well as B to A

Now i want to put these two machines in a Separate network without changing the IP ADDRESS&netmask.How to do that?.(if machines are in physically sepated network they should not excahnge packets using dev as my case.They can use only gateway).
Simply speaking I shud not be able to ping form A to B or vice versa if they are separate network) . Without using gateway I want to achieve the goal.
Any ideas.Thanks in advance

Machines belong to the same network for more than one reason. There is the physical connection. If they are not separated by a router function, then they are onthe same network. The second item to consider is the ip addresses. 192.168.1.x is a private ip network. class C. The addresses you are using belong to the same network. To change them to different networks, you will have to change the ip address of one. You could leave A as 192.168.1.1 and change B to 192.168.2.X.

If you change ip addresses you will have to do routing between the machines, assuming you do want them to talk.

Hope this helps.

Let me get U a clear picture.
If u want to connect from one network to another u can do routing by two ways.
one is
route add -net 192.168.0.0 netmask 255.255.255.0 dev eth0

another one is

route add -net 192.168.0.0 netamask 255.255.255.0 gw 192.168.1.1
(ip_forward is enabled)
MY QUESTION IS
packets should be sent to another network only if routing is done using gateway.
Packets should not be sent to another network if the routing is done using dev.
how to do that?
in my case if the routing is done using dev they are not a physically sepated network.I can call them physically separate one only if they are talking using a gateway