OL 9 must not forward Internet Protocol version 4 (IPv4) source-routed packets.

Source-routed packets allow the source of the packet to suggest routers forward the packet along a different path than configured on the router, which can be used to bypass network security measures. This requirement applies only to the forwarding of source-routed traffic, such as when IPv4 forwarding is enabled and the system is functioning as a router.

Accepting source-routed packets in the IPv4 protocol has few legitimate uses. It must be disabled unless it is absolutely required.

Verify that OL 9 will not accept IPv4 source-routed packets.

Check the value of the all "accept_source_route" variables with the following command:

$ sysctl net.ipv4.conf.all.accept_source_route net.ipv4.conf.all.accept_source_route = 0

If the returned line does not have a value of "0", a line is not returned, or the line is commented out, this is a finding.

Configure OL 9 to ignore IPv4 source-routed packets.

Add or edit the following line in a single system configuration file in the "/etc/sysctl.d/" directory:

net.ipv4.conf.all.accept_source_route = 0

Load settings from all system configuration files with the following command:

$ sudo sysctl --system