How to enable IP forwarding in Linux

IP forwarding also is known as IP routing or Internet routing is a process used to determine which path a packet or datagram can be sent. The process uses routing information to make decisions and is designed to send a packet over multiple networks.

Generally, networks are separated from each other by routers. For packets to travel between networks, they must be “routed” from one network to another. These routers contain a routing table that can contain specific instructions on how to send packets to a destination network (known as a route), or a set of generic instructions on where to send packets that do not match any of the other specified routes (called a default route), or both. These routes can either be hard-coded into the router by the network administrator (called a static route) or learned dynamically via a routing protocol. These routes give the routers instructions on how to utilize the physical network infrastructure that is in place to get packets to their destination, regardless of the number of hops that they must take to get there.

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

net.ipv4.ip_forward=1

net.ipv6.conf.all.forwarding=1

Apply the change

sysctl –p /etc/sysctl.conf

cat /proc/sys/net/ipv4/ip_forward

echo “0” > /proc/sys/net/ipv4/ip_forward