manual/generic/linux/ip-forwarding

Description

Test if Kernel IP forwarding works.

SUT(system under test) should has at least two Ethernet ports. Assume you use SUT_eth0 and SUT_eth1 here.
Make sure iptables package installed on SUT.
Boot SUT and test client to OS.
Run "sudo su -" to switch to root user.
Run "ip addr show" to check if the ports used for testing are detected.
Do the following steps on SUT to set test environment and enable ip_forward.
Connect SUT_eth1 to router0 that connected to internet. Assume the gateway IP is 10.0.0.1.
Connect SUT_eth0 to router1 that used for private network.
Execute "dhclient eth1" to get a IP address or set IP for it manually.
Execute "ping -I eth1 10.0.0.1" and "ping -I eth1 8.8.8.8" to check if eth1 is set properly.
ip link set eth0 down
ip addr add 192.168.1.1/24 dev eth0
ip link set eth0 up
echo 1 > /proc/sys/net/ipv4/conf/all/forwarding
iptables -t nat -A POSTROUTING -o eth1 -j MASQUERADE
iptables -A FORWARD -i eth0 -j ACCEPT
Do the following steps on test client to test if Kernel IP forwarding works.
Connect test client eth0 port to the private route1.
ip link set eth0 down
ip addr add 192.168.1.2/24 dev eth0
ip link set eth0 up
ip route add default via 192.168.1.1
ping 10.0.0.1
ping 8.8.8.8