I have 4 Linux machines(Debian woody) A,B,C.
A and B are in same network.(192.168.1.0/24 )
C and D are in diffrent network.(192.168.0.0/24)


192.168.1.2/24

A ---------------------------------------------------> B
192.168.1.1/24 (Gateway)


192.168.0.2/24
D------------------------------------------------------->C
192.168.0.1/24 (Gateway)


B and C are configures as gateways.

For A , machine B is the default gateway.
For D , machine C is the default gateway.
Now I want to connect From machine A to Machine D and vice versa using their respective gateways(B and C).
MY routing is like this
In machine A
---------------------
route add default gw 192.168.1.1
In machine D
---------------------
route add default gw 192.168.0.1
In machine B(gateway)
---------------------------------
route add -net 192.168.0.0 netmask 255.255.255.0 dev eth0

In machine C(another gateway)
-------------------------------------------
route add 192.168.1.1 dev eth0
route add -net 192.168.1.0 netmask 255.255.255.0 dev eth0

----- After this I am able to connect from one network to another.
One of my friend said that This is not the correct way of routing.These two networks are not physically separarted.By routing only I separated the network.He said another way of routing is there.I searched on net.But didn't get any ideas.Can Any help me.And explain it.Any routing guides are there?.

The problem with your setup is that you only configure two networks while the actual setup has three networks.

A & B are on one network say 192.168.1.0/24
B & C are on another network, your backbone. Call it 192.168.0.0/24
C & D are on the third network. 192.168.2.0/24

There can't be two networks using the same IP network as in your configuration.
The network you forgot is the one that B & C share.
On B you say that B is directly connected to network 192.168.0.0 network, but on C you say that the same network is 192.168.1.0, provided that both B & C use eth0 to connect to the other gateway.

Had to leave the computer for a brief moment.

Let say your setup is like this:
A (192.168.1.2) - (192.168.1.1)eth1 B (192.168.0.1)eth0 - (192.168.0.2)eth0 C (192.168.2.1)eth1 - (192.168.2.2) C

Then you setup for the various machines would be:
A
route add default gw 192.168.1.1
route add -net 192.168.1.0 netmask 255.255.255.0 dev eth0

B
route add -net 192.168.0.0 netmask 255.255.255.0 dev eth0
route add -net 192.168.1.0 netmask 255.255.255.0 dev eth1
route add -net 192.168.2.0 netmask 255.255.255.0 dev eth0 gw 192.168.0.2

C
route add -net 192.168.0.0 netmask 255.255.255.0 dev eth0
route add -net 192.168.2.0 netmask 255.255.255.0 dev eth1
route add -net 192.168.1.0 netmask 255.255.255.0 dev eth0 gw 192.168.0.1

D
route add default gw 192.168.2.1
route add -net 192.168.2.0 netmask 255.255.255.0 dev eth0

This should work. Some of the work may already be done at your computers by their network startup scripts.
Probably you will only have to add the route add -net 192.***** gw 192.168.0*** lines to B & C.

[QUOTE]Originally posted by ugge
The problem with your setup is that you only configure two networks while the actual setup has three networks.

A & B are on one network say 192.168.1.0/24
B & C are on another network, your backbone. Call it 192.168.0.0/24
C & D are on the third network. 192.168.2.0/24

There can't be two networks using the same IP network as in your configuration.
The network you forgot is the one that B & C share.
On B you say that B is directly connected to network 192.168.0.0 network, but on C you say that the same network is 192.168.1.0, provided that both B & C use eth0 to connect to the other gateway. [/QUOTE


What u r meaning by saying "There can't be two networks using the same IP network as in your configuration."
In my case A and B are in 192.168.1.0/24 network
C and D are in 192.168.0.0/24 network.
How u r saying they are using the same IP network

Both B and C have two NICs, right?
The two cards need to be connected to different networks, that is different IP networks, like 192.168.0.0 and 192.168.1.0 for example.

That way if you count your networks, you need three as I mentioned earlier.

yes exactly!What u said is correct.My gateways have got two NIC's.But the gateways also not in the same IP network.Putting it simply I don't have 3 networks.IT is 4 networks.

A eth0 -192.168.1.2

B -eth0 -192.168.1.1/24
eth1 -172.16.1.1/255.255.0.0

C- eth0 -192.168.0.1/24
eth1-172.17.5.5/255.255..0.0

D- eth0 192.168.0.2

Here only I have routing problem

Well, then you have to tweak the configuration for B & C accordingly.
For B that would be
[b]route add -net 192.168.0.0 netmask 255.255.255.0 dev eth1 gw <gateway of 172.16.1.0 network>

fine.