Messages in this thread | | | Date | Mon, 14 Sep 2009 17:10:01 +0200 | From | Stephan von Krawczynski <> | Subject | Re: ipv4 regression in 2.6.31 ? |
| |
On Mon, 14 Sep 2009 15:57:03 +0200 Eric Dumazet <eric.dumazet@gmail.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@eth0 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@eth0 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@eth0, 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.
Problem is this: Kernel 2.6.30.X and below work flawlessly in this setup, only kernel 2.6.31 acts different. Is this an intended change in policy?
-- Regards, Stephan -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |