A Linux server has been configured as a gateway to allow local LAN access to the Internet. Users can ping the gateway address but cannot access the Internet. After further troubleshooting, it has been determined that IP forwarding is not enabled on the Linux server. Which of the following commands will enable routing?

A.
route add IP_FORWARD eth0

B.
echo "1" > /proc/sys/net/ipv4/ip_forward

C.
sysctl -n net.ipv4.conf.eth0.forwarding = 1

D.
sysctl -a net.ipv4.conf.forwarding = 1