If your machine would not exist, the last router _before_ your machine would send an ICMP not reachable message.

Doing strange things with your ICMP config buys you absolutely nothing in respect to an attacker, but may easily make legitimate network use more difficult. E.g. look how MTU discovery works and how it does not because “wise” admins disallow their machines to send ICMP replys.

Regards,
Jim

don’t ignore ICMP echos:
sysctl -w net.ipv4.icmp_echo_ignore_all=0

do ignore ICMP echos:
sysctl -w net.ipv4.icmp_echo_ignore_all=1

sysctl -a will give you a nice list of values that you can tweak.

If you’re running a Redhat-based system, you can plop the desired values in /etc/sysctl.conf.