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The system must use a reverse-path filter for IPv4 network traffic when possible on all interfaces.


Finding ID Version Rule ID IA Controls Severity
V-217924 RHEL-06-000096 SV-217924r505923_rule Medium
Enabling reverse path filtering drops packets with source addresses that should not have been able to be received on the interface they were received on. It should not be used on systems which are routers for complicated networks, but is helpful for end hosts and routers serving small networks.
Red Hat Enterprise Linux 6 Security Technical Implementation Guide 2020-09-03


Check Text ( C-19405r376787_chk )
The status of the "net.ipv4.conf.all.rp_filter" kernel parameter can be queried by running the following command:

$ sysctl net.ipv4.conf.all.rp_filter
net.ipv4.conf.all.rp_filter = 1

$ grep net.ipv4.conf.all.rp_filter /etc/sysctl.conf /etc/sysctl.d/*
net.ipv4.conf.all.rp_filter = 1

If "net.ipv4.conf.all.rp_filter" is not configured in the /etc/sysctl.conf file or in the /etc/sysctl.d/ directory, is commented out or does not have a value of "1", this is a finding.
Fix Text (F-19403r376788_fix)
To set the runtime status of the "net.ipv4.conf.all.rp_filter" kernel parameter, run the following command:

# sysctl -w net.ipv4.conf.all.rp_filter=1

Set the system to the required kernel parameter by adding the following line to "/etc/sysctl.conf" or a config file in the /etc/sysctl.d/ directory (or modify the line to have the required value):

net.ipv4.conf.all.rp_filter = 1

Issue the following command to make the changes take effect:

# sysctl --system