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    SubjectRe: ipv4 regression in 2.6.31 ?
    On Wed, 16 Sep 2009 05:23:04 +0000
    Jarek Poplawski <jarkao2@gmail.com> wrote:

    > On Tue, Sep 15, 2009 at 03:57:19PM -0700, Stephen Hemminger wrote:
    > > On Tue, 15 Sep 2009 08:13:55 +0000
    > > Jarek Poplawski <jarkao2@gmail.com> wrote:
    > >
    > > > On 14-09-2009 18:31, Stephen Hemminger wrote:
    > > > > On Mon, 14 Sep 2009 17:55:05 +0200
    > > > > Stephan von Krawczynski <skraw@ithnet.com> wrote:
    > > > >
    > > > >> On Mon, 14 Sep 2009 15:57:03 +0200
    > > > >> Eric Dumazet <eric.dumazet@gmail.com> wrote:
    > > > >>
    > > > >>> Stephan von Krawczynski a A~(c)crit :
    > > > >>>> Hello all,
    > > > ...
    > > > >>> 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.
    > > > ...
    > > > > RP filter did not work correctly in 2.6.30. The code added to to the loose
    > > > > mode caused a bug; the rp_filter value was being computed as:
    > > > > rp_filter = interface_value & all_value;
    > > > > So in order to get reverse path filter both would have to be set.
    > > > >
    > > > > In 2.6.31 this was change to:
    > > > > rp_filter = max(interface_value, all_value);
    > > > >
    > > > > This was the intended behaviour, if user asks all interfaces to have rp
    > > > > filtering turned on, then set /proc/sys/net/ipv4/conf/all/rp_filter = 1
    > > > > or to turn on just one interface, set it for just that interface.
    > > >
    > > > Alas this max() formula handles also cases where both values are set
    > > > and it doesn't look very natural/"user friendly" to me. Especially
    > > > with something like this: all_value = 2; interface_value = 1
    > > > Why would anybody care to bother with interface_value in such a case?
    > > >
    > > > "All" suggests "default" in this context, so I'd rather expect
    > > > something like:
    > > > rp_filter = interface_value ? : all_value;
    > > > which gives "the inteded behaviour" too, plus more...
    > > >
    > > > We'd only need to add e.g.:
    > > > 0 - Default ("all") validation. (No source validation if "all" is 0).
    > > > 3 - No source validation on this interface.
    > >
    > > More values == more confusion.
    > > I chose the maxconf() method to make rp_filter consistent with other
    > > multi valued variables (arp_announce and arp_ignore).
    >
    > This additional value is not necessary (it'd give as superpowers).
    > Max seems logical to me only when values are sorted (especially if
    > max is the strictest).

    The values had to be unsorted because of the requirement to retain
    interface compatibility with older releases.
    --


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