From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jarek Poplawski Subject: Re: ipv4 regression in 2.6.31 ? Date: Wed, 16 Sep 2009 05:23:04 +0000 Message-ID: <20090916052304.GA4894@ff.dom.local> References: <20090914093128.4d709ff6@nehalam> <20090915081354.GA10037@ff.dom.local> <20090915155719.22bae41e@nehalam> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: David Miller , Stephan von Krawczynski , Eric Dumazet , linux-kernel@vger.kernel.org, Linux Netdev List To: Stephen Hemminger Return-path: Content-Disposition: inline In-Reply-To: <20090915155719.22bae41e@nehalam> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On Tue, Sep 15, 2009 at 03:57:19PM -0700, Stephen Hemminger wrote: > On Tue, 15 Sep 2009 08:13:55 +0000 > Jarek Poplawski wrote: > > > On 14-09-2009 18:31, Stephen Hemminger wrote: > > > On Mon, 14 Sep 2009 17:55:05 +0200 > > > Stephan von Krawczynski wrote: > > > > > >> On Mon, 14 Sep 2009 15:57:03 +0200 > > >> Eric Dumazet 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). Jarek P. > > -------- > Subject: [PATCH] Document rp_filter behaviour > > Signed-off-by: Stephen Hemminger > > > --- a/Documentation/networking/ip-sysctl.txt 2009-09-15 15:54:25.844934373 -0700 > +++ b/Documentation/networking/ip-sysctl.txt 2009-09-15 15:55:40.709205883 -0700 > @@ -744,6 +744,8 @@ rp_filter - INTEGER > Default value is 0. Note that some distributions enable it > in startup scripts. > > + The max value from conf/{all,interface}/rp_filter is used. > + > arp_filter - BOOLEAN > 1 - Allows you to have multiple network interfaces on the same > subnet, and have the ARPs for each interface be answered > > > > > > > > --