Your server has two fully functional NICs with correct IP configuration. The server is not forwarding traffic between the NICs. Which command will enable forwarding properly?

A.
setparam 1 > /proc/sys/net/ipv4/ip_autoconfig

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

C.
cat $1 > /proc/sys/net/ethernet

D.
set $=1 /proc/sys/net/ipv4/route

Explanation:
See http://www.ibm.com/developerworks/linux/library/l-proc.html
# cat /proc/sys/net/ipv4/ip_forward
0
# echo "1" > /proc/sys/net/ipv4/ip_forward

Remember that this solution is working only until reboot, use sysctl to set ip_forwarding permanently.