Subject: Re: Linux vs FreeBSD Which is correct.

From: Stephen Clark <[email-masked]>
Date: Fri, 19 Aug 2011 15:10:14 -0400

On 08/19/2011 12:18 PM, Chris Friesen wrote:
> On 08/18/2011 06:42 AM, Stephen Clark wrote:
>
>> 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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