to prevent IP spoofing from DDos attacks. If using asymmetric routing
or other complicated routing, then loose mode is recommended.
- conf/all/rp_filter must also be set to non-zero to do source validation
- on the interface
+ The max value from conf/{all,interface}/rp_filter is used
+ when doing source validation on the {interface}.
Default value is 0. Note that some distributions enable it
in startup scripts.