Re: Linux vs FreeBSD Which is correct.

On 08/19/2011 12:18 PM, Chris Friesen wrote:

On 08/18/2011 06:42 AM, Stephen Clark wrote:

quoted

I guess I don't really understand what reverse path filter stuff is all
about, much less making it weaker.
But using 2 made the pings responses be seen.

It's described in RFC3704.  The idea is to block spoofed packets.

From Documentation/networking/ip-sysctl.txt:

rp_filter - INTEGER
0 - No source validation.
1 - Strict mode as defined in RFC3704 Strict Reverse Path
    Each incoming packet is tested against the FIB and if the interface
    is not the best reverse path the packet check will fail.
    By default failed packets are discarded.
2 - Loose mode as defined in RFC3704 Loose Reverse Path
    Each incoming packet's source address is also tested against the FIB
    and if the source address is not reachable via any interface
    the packet check will fail.

   Current recommended practice in RFC3704 is to enable strict mode
   to prevent IP spoofing from DDos attacks. If using asymmetric routing
   or other complicated routing, then loose mode is recommended.

   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.

Thanks for taking the time to explain this. Much appreciated.


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