for i in /proc/sys/net/ipv4/*/rp_filter; do echo 1 > $f done Or simply echo 1 > /proc/sys/net/ipv4/*/rp_filter (depends on your shell) This compares the source adress against the routing table More info about the ~50 options you can find at /usr/src/linux/Documentation/networking/ip-sysctl.txt