A single Nic redhat7.2linux uses iptables as a simple gateway configuration

Article title: use iptables in a single Nic redhat7.2linux as a simple gateway configuration. Linux is a technology channel of the IT lab in China. Includes basic categories such as desktop applications, Linux system management, kernel research, embedded systems, and open source.
Author: ken
　　
　　
Because the default kernel modules is not installed
The ipchains: Protocol not available error occurs during use. do not think that 7.2 is regressing.
More powerful iptables has been used to build a firewall.
　　
Environment: The intranet is 192.168.2.0, and the Internet DDN is 10.19.78.0. The Internet gateway is 10.19.78.1.
The intranet IP address of the configured gateway server is 192.168.2.170, the Internet IP address is 10.19.78.5, and the two addresses are bound to one
Block Nic (dual Nic is better ).
　　
Change permanent file configuration
(1) modify/etc/sysconfig/network
　　
NETWORKING = yes
FORWARD_IPV4 = yes
HOSTNAME = server
GATEWAY = 10.19.78.1
GATEWAYDEV = eth0
　　
# The Gateway is 10.19.78.1
　　
(2) create a file ifcfg-eth1 under the/etc/sysconfig/network-scripts directory
　　
DEVICE = eth1
USERCTL = no
ONBOOT = yes
BOOTPROTO =
BROADCAST = 10.19.78.7
NETWORK = 10.19.78.0
NETMASK = 255.255.255.255.248
IPADDR = 10.19.78.5 # ip address of the local machine in the upper-level network
　　
(3) use/ect/rc. d/init. d/inet restart to make the IP configuration take effect.
　　
(4) use iptables to write the following script gw. sh:
　　
# Begin
　　
Echo 1>/proc/sys/net/ipv4/ip_forward
　　
Modprobe iptable_nat
Modprobe ip_conntrack
Modprobe ip_conntrack_ftp
　　
Iptables-F INPUT
　　
Iptables-F FORWARD
　　
Iptables-f postrouting-t nat
　　
Iptables-t nat-F
　　
Iptables-P FORWARD DROP
　　
Iptables-a forward-s 192.168.2.0/24-j ACCEPT
　　
Iptables-a forward-I eth1-m state -- state ESTABLISHED, RELATED-j ACCEPT
　　
Iptables-t nat-a postrouting-o eth1-s 192.168.2.0/24-j SNAT -- to 10.19.78.5
　　
# End
　　
　　
Change gw. sh to an executable permission to run. other machines can access the internet using the gateway! You can also add
/Ect/rc. d/rc. local is used to run automatically upon startup.
This is the simplest function of using iptables. to build a powerful firewall, you can view it on your own.