Configure Linux For nating eaisly

Step by Step Procedure

Step 1. Add 2 Network cards to the Linux box

Step 2. Verify the Network cards, check if they installed properly or not

Step 3. Configure eth0 for Internet with a Public (External network or Internet)

# cat ifcfg-eth0

DEVICE=eth0
BOOTPROTO=static
IPADDR=X.X.X.X
NETMASK=255.255.255.0
NETWORK=X.X.X.0
ONBOOT=yes
TYPE=Ethernet
USERCTL=no
IPV6INIT=no
PEERDNS=yes
GATEWAY=X.X.X.X # Provided by the ISP

Step 4. Configure eth1 for LAN with a local IP (Internal private network)
# cat ifcfg-eth1

BOOTPROTO=none
PEERDNS=yes
TYPE=Ethernet
IPV6INIT=no
DEVICE=eth1
NETMASK=255.255.0.0
BROADCAST=""
IPADDR=192.168.1.1
NETWORK=192.168.0.0
USERCTL=no
ONBOOT=yes

Step 5. Gateway Configuration
# cat /etc/sysconfig/network

NETWORKING=yes
HOSTNAME=nat
GATEWAY=X.X.X.1

Step 6. DNS Configuration
# cat /etc/resolv.conf

nameserver 4.2.2.2 # DNS Server


Step 7. NAT configuration with IP Tables
First of all you have to flush and delete existing firewall rules. So flush rules by typing in terminal:

iptables -F
iptables -t nat -F
iptables -t mangle -F

Now delete these chains:

iptables -X
iptables -t nat -X
iptables -t mangle -X

# Set up IP FORWARDing and Masquerading

iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE
iptables -A FORWARD -i eth1 -j ACCEPT

# Enables packet forwarding by kernel (save this setting in /etc/sysctl.conf file)

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

#Apply the configuration

service iptables save
service iptables restart

# Check if iptables is set to start during boot up

chkconfig –list iptables

Step 8. Testing

Go to Client Machine
ping local LAN gateway ie local ip of linux server

Hurrey
its Done