hhhhmmmm....
so i can understand that we can configure our host machine better then virtual machine.
& " I would like to say that there is nothing difference b/w CentOS, Red Hat & Fedora regarding file locations, commands,configuration etc... But I can assume some of the minor difference, Which I have not see yet"

So its decided that I am going to configure my host machine's second NIC "eth1" as a router & I'll post all the configurations & hope you'll guide me...
Thanks allot ,,,,....

---------- Post updated 02-04-12 at 02:05 AM ---------- Previous update was 02-03-12 at 09:03 PM ----------

Yes I done it...
I configure my Linux machine to behave like a router.
Configurations are as follow!

First we need to enable packet forwarding on the kernel level. So append the following two lines in /etc/sysctl.conf file:

Code:

# vim /etc/sysctl.conf

Code:

# Controls IP packet forwarding
net.ipv4.ip_forward = 1

Now Configure your interface with the following parameters, In my case the interface was eth1 you may follow yours, So I apply this command to make changes/to set the parameters:

Code:

# vim /etc/sysconfig/network-scripts/ifcfg-eth1

Parameters for the eth1 file should like this:

Code:

DEVICE=eth1
BOOTPROTO=none
IPADDR=10.3.20.1
IPV6INIT=no
ONBOOT=yes
NAME=eth1
NETMASK=255.255.255.0
HWADDR=00:04:75:EB:D0:A3
TYPE=Ethernet
PREFIX=24
GATEWAY=10.3.20.1
DEFROUTE=yes
IPV4_FAILURE_FATAL=yes
UUID=9c92fad9-6ecb-3e6c-eb4d-8a47c6f50c04

Now add the route followed by the command:

Code:

# route add -net 10.3.20.0 netmask 255.255.255.0 gw 10.3.20.1 dev eth1

To define the routing for the 10.3.20.0 network on the 10.3.20.1 interface (eth1) open the file:

Code:

# vim /etc/sysconfig/network-scripts/route-eth1

IN this file append the following line:

Code:

10.3.20.0/24 via 10.3.20.1

Now restart the network service with the following command:

Code:

# service network restart

Check the new route with the following command:

Code:

# route -n

In my case the outputs was like this:

Code:

[root@rash ~]# route -n
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
10.3.20.0       0.0.0.0         255.255.255.0   U     1      0        0 eth1
192.168.15.0    0.0.0.0         255.255.255.0   U     1      0        0 eth0
192.168.122.0   0.0.0.0         255.255.255.0   U     0      0        0 virbr0
0.0.0.0         192.168.15.1    0.0.0.0         UG    0      0        0 eth0
You have new mail in /var/spool/mail/root

You may easily find the new route in these information.
Conguratulations with this guide you have configured your Linux machine to act as a router.