Information
The net.ipv4.ip_forward and net.ipv6.conf.all.forwarding flags are used to tell the system whether it can forward packets or not.
Setting net.ipv4.ip_forward and net.ipv6.conf.all.forwarding to 0 ensures that a system with multiple interfaces (for example, a hard proxy), will never be able to forward packets, and therefore, never serve as a router.
Solution
Set the following parameter in /etc/sysctl.conf or a file in /etc/sysctl.d/ ending inconf :
- net.ipv4.ip_forward = 0
Example:
# printf '%s
' "net.ipv4.ip_forward = 0" >> /etc/sysctl.d/60-netipv4_sysctl.conf
Run the following script to set the active kernel parameters:
#!/usr/bin/env bash
{
sysctl -w net.ipv4.ip_forward=0
sysctl -w net.ipv4.route.flush=1
}
- IF - IPv6 is enabled on the system:
Set the following parameter in /etc/sysctl.conf or a file in /etc/sysctl.d/ ending inconf :
- net.ipv6.conf.all.forwarding = 0
Example:
# printf '%s
' "net.ipv6.conf.all.forwarding = 0" >> /etc/sysctl.d/60-netipv6_sysctl.conf
Run the following script to set the active kernel parameters:
#!/usr/bin/env bash
{
sysctl -w net.ipv6.conf.all.forwarding=0
sysctl -w net.ipv6.route.flush=1
}
Note: If these settings appear in a canonically later file, or later in the same file, these settings will be overwritten
Impact:
IP forwarding is required on systems configured to act as a router. If these parameters are disabled, the system will not be able to perform as a router.
Many Cloud Service Provider (CSP) hosted systems require IP forwarding to be enabled. If the system is running on a CSP platform, this requirement should be reviewed before disabling IP forwarding.