The Linux kernel is flexible, and the way it works can be modified on the fly by dynamically changing some of its parameters using the sysctl command.

• sysctl can be used to both read and write sysctl data; i.e. it provides an interface that allows the examination and change of several hundred kernel parameters in Linux.
• Changes take effect immediately, and there is even a way to make them persist after a reboot.
  • The parameters available are those listed under /proc/sys/.

sudo cp /etc/sysctl.conf /etc/sysctl.conf.orig

sudo vi /etc/sysctl.conf

Remove the hash sign in front of certain command lines to stop some spoofing attacks and enhance other security measures:

/etc/sysctl.conf

net.ipv4.conf.default.rp_filter=1
net.ipv4.conf.all.rp_filter=1
net.ipv4.tcp_syncookies=1
net.ipv4.icmp_echo_ignore_broadcasts = 1
net.ipv4.icmp_ignore_bogus_error_responses = 1
net.ipv4.conf.all.accept_redirects = 0
net.ipv4.conf.all.send_redirects = 0
net.ipv4.conf.all.accept_source_route = 0
 
net.ipv6.conf.all.accept_redirects = 0
net.ipv6.conf.all.accept_source_route = 0

Save the /etc/sysctl.conf file.

This reloads the sysctl parameters:

sudo sysctl -p