IP forwarding for IPv4 must not be enabled, unless the system is a router.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-50967	OL6-00-000082	SV-65173r1_rule		Medium

Description
IP forwarding permits the kernel to forward packets from one network interface to another. The ability to forward packets between two networks is only appropriate for routers.

STIG	Date
Oracle Linux 6 Security Technical Implementation Guide	2014-06-12

Details

Check Text ( C-53419r1_chk )
If the system serves as a router, this is not applicable. The status of the "net.ipv4.ip_forward" kernel parameter can be queried by running the following command: $ sysctl net.ipv4.ip_forward The output of the command should indicate a value of "0". If this value is not the default value, investigate how it could have been adjusted at runtime, and verify it is not set improperly in "/etc/sysctl.conf". If the correct value is not returned, this is a finding.

Check Text ( C-53419r1_chk )

If the system serves as a router, this is not applicable.

The status of the "net.ipv4.ip_forward" kernel parameter can be queried by running the following command:

$ sysctl net.ipv4.ip_forward

The output of the command should indicate a value of "0". If this value is not the default value, investigate how it could have been adjusted at runtime, and verify it is not set improperly in "/etc/sysctl.conf".
If the correct value is not returned, this is a finding.

Fix Text (F-55771r1_fix)
To set the runtime status of the "net.ipv4.ip_forward" kernel parameter, run the following command: # sysctl -w net.ipv4.ip_forward=0 If this is not the system's default value, add the following line to "/etc/sysctl.conf": net.ipv4.ip_forward = 0