whether and how setup should adjust the reverse path filtering mechanism for the physical devices to be used. Values are %unchanged (to leave it alone) or 0, 1, 2 (values to set it to). the documentation in kernel source (Documentation/networking/ip-sysctl.txt) says:
rp_filter - BOOLEAN
1 - do source validation by reversed path, as specified in RFC1812
Recommended option for single homed hosts and stub network
routers. Could cause troubles for complicated (not loop free)
networks running a slow unreliable protocol (sort of RIP),
or using static routes.
0 - No source validation.
conf/all/rp_filter must also be set to TRUE to do source validation
on the interface
Default value is 0. Note that some distributions enable it
in startup scripts.
