3.1.2 Ensure packet redirect sending is disabled (Scored)

Level 1 - Server
Level 1 - Workstation 

ICMP Redirects are used to send routing information to other hosts. As a host itself does not act as a router (in a host only configuration), there is no need to send redirects.

An attacker could use a compromised host to send invalid ICMP redirects to other router devices in an attempt to corrupt routing and have users access a system set up by the attacker as opposed to a valid system.

Run the following command and verify output matches:

# sysctl net.ipv4.conf.all.send_redirects 
net.ipv4.conf.all.send_redirects = 0 
# sysctl net.ipv4.conf.default.send_redirects 
net.ipv4.conf.default.send_redirects = 0

Set the following parameter in the “/etc/sysctl.conf” file:

net.ipv4.conf.all.send_redirects = 0 
net.ipv4.conf.default.send_redirects = 0

Run the following commands to set the active kernel parameters:

# sysctl -w net.ipv4.conf.all.send_redirects=0 
# sysctl -w net.ipv4.conf.default.send_redirects=0 
# sysctl -w net.ipv4.route.flush=1