Linux Internet Gateway Server Setup

Setup Netwok Diagram.

Linux Server:

eth0 ( External Interface )
eth1 ( Internal Netwok Interface) ( 192.168.1.X series )

Step 1. Enable ip nat in linux kernel.

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

Step 2. Assign IP address to eth0 and eth1
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/etc/sysconfig/network-scripts/ifcfg-eth0

DEVICE=eth0
ONBOOT=yes
IPADDR=xxx.xxx.xxx.xxx
NETMASK=255.255.255.xxx
GATEWAY=xxx.xxx.xxx.xxx
TYPE=Ethernet
BOOTPROTO=static
HWADDR=00:11:5B:F6:E2:5D
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/etc/sysconfig/network-scripts/ifcfg-eth1

DEVICE=eth1
ONBOOT=yes
IPADDR=192.168.1.1
NETMASK=255.255.255.0
TYPE=Ethernet
BOOTPROTO=static
HWADDR=00:29:5X:FG:32:8S
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"service network restart"

Step 3. Set iptable commands.

"iptables -F"
"iptables --table nat --append POSTROUTING --out-interface eth0 -j MASQUERADE"
"iptables --append FORWARD --in-interface eth1 -j ACCEPT"

Step 4. Add the above entries to /etc/rc.local file.

/etc/rc.local

/sbin/iptables -F 2>/dev/null
/sbin/iptables --table nat --append POSTROUTING --out-interface eth0 -j MASQUERADE 2>/dev/null
/sbin/iptables --append FORWARD --in-interface eth1 -j ACCEPT 2>/dev/null

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