Хотя у меня в rc.ip_forward написано примерно так:
# Start IP packet forwarding:
ip_forward_start() {
if [ -f /proc/sys/net/ipv4/ip_forward ]; then
echo "Activating IPv4 packet forwarding."
echo 1 > /proc/sys/net/ipv4/ip_forward
fi
# When using IPv4 packet forwarding, you will also get the
# rp_filter, which automatically rejects incoming packets if the
# routing table entry for their source address doesn't match the
# network interface they're arriving on. This has security
# advantages because it prevents the so-called IP spoofing,
# however it can pose problems if you use asymmetric routing
# (packets from you to a host take a different path than packets
# from that host to you) or if you operate a non-routing host
# which has several IP addresses on different interfaces. To
# turn rp_filter off, uncomment the lines below:
#if [ -r /proc/sys/net/ipv4/conf/all/rp_filter ]; then
# echo "Disabling rp_filter."
# echo 0 > /proc/sys/net/ipv4/conf/all/rp_filter
#fi
}