This is a very good thread
handling /proc/sys/net/ipv4 values.
You might want to add
for f in /proc/sys/net/ipv4/conf/*/accept_source_route; do
echo 0 > $f
for f in /proc/sys/net/ipv4/conf/*/log_martians; do
echo 1 > $f
for disallowing source routed traffic which shouldnt happen, and add logging for some weird packets.
Ofcourse you could enter 'em, or just stuff em in a startup sequence script like /etc/rc.d/rc.sysinit /etc/rc.S or whatever your distro uses. Another way is using sysctl, add the values to /etc/sysctl.conf if your distro uses that.