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Date: Mon, 14 Sep 2009 17:55:05 +0200 From: Stephan von Krawczynski <skraw@...net.com> To: Eric Dumazet <eric.dumazet@...il.com> Cc: linux-kernel@...r.kernel.org, davem@...emloft.net, Linux Netdev List <netdev@...r.kernel.org> Subject: Re: ipv4 regression in 2.6.31 ? On Mon, 14 Sep 2009 15:57:03 +0200 Eric Dumazet <eric.dumazet@...il.com> wrote: > Stephan von Krawczynski a écrit : > > Hello all, > > > > today we experienced some sort of regression in 2.6.31 ipv4 implementation, or > > at least some incompatibility with former 2.6.30.X kernels. > > > > We have the following situation: > > > > ---------- vlan1@...0 192.168.2.1/24 > > / > > host A 192.168.1.1/24 eth0 -------<router> host B > > \ > > ---------- eth1 192.168.3.1/24 > > > > > > Now, if you route 192.168.1.0/24 via interface vlan1@...0 on host B and let > > host A ping 192.168.2.1 everything works. But if you route 192.168.1.0/24 via > > interface eth1 on host B and let host A ping 192.168.2.1 you get no reply. > > With tcpdump we see the icmp packets arrive at vlan1@...0, but no icmp echo > > reply being generated neither on vlan1 nor eth1. > > Kernels 2.6.30.X and below do not show this behaviour. > > Is this intended? Do we need to reconfigure something to restore the old > > behaviour? > > > > Asymetric routing ? > > Check your rp_filter settings > > grep . `find /proc/sys/net -name rp_filter` > > 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. > > conf/all/rp_filter must also be set to non-zero to do source validation > on the interface > > Default value is 0. Note that some distributions enable it > in startup scripts. Ok, here you can see 2.6.31 values from the discussed box: (remember, no ping reply in this setup) /proc/sys/net/ipv4/conf/all/rp_filter:1 /proc/sys/net/ipv4/conf/default/rp_filter:0 /proc/sys/net/ipv4/conf/lo/rp_filter:0 /proc/sys/net/ipv4/conf/eth2/rp_filter:0 /proc/sys/net/ipv4/conf/eth0/rp_filter:0 /proc/sys/net/ipv4/conf/eth1/rp_filter:0 /proc/sys/net/ipv4/conf/vlan1/rp_filter:0 And these are from the same box with 2.6.30.5: (ping reply works) /proc/sys/net/ipv4/conf/all/rp_filter:1 /proc/sys/net/ipv4/conf/default/rp_filter:0 /proc/sys/net/ipv4/conf/lo/rp_filter:0 /proc/sys/net/ipv4/conf/eth2/rp_filter:0 /proc/sys/net/ipv4/conf/eth0/rp_filter:0 /proc/sys/net/ipv4/conf/eth1/rp_filter:0 /proc/sys/net/ipv4/conf/vlan1/rp_filter:0 As you can see they're all the same. Does this mean that rp_filter never really worked as intended before 2.6.31 ? Or does it mean that rp_filter=0 (eth1 and vlan1) gets overriden by all/rp_filter=1 in 2.6.31 and not before? -- Regards, Stephan -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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