From mboxrd@z Thu Jan 1 00:00:00 1970 From: Hannes Frederic Sowa Subject: Re: [patch net] ipv6: do not create neighbor entries for local delivery Date: Thu, 8 Aug 2013 22:16:28 +0200 Message-ID: <20130808201627.GI14001@order.stressinduktion.org> References: <20130130082608.GA1604@minipsycho.orion> <20130808194702.GH14001@order.stressinduktion.org> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 To: Debabrata Banerjee , Jiri Pirko , mleitner@redhat.com, "davem@davemloft.net" , "netdev@vger.kernel.org" , Alexey Kuznetsov , "jmorris@namei.org" , "yoshfuji@linux-ipv6.org" , Patrick McHardy , "Banerjee, Debabrata" , Joshua Hunt Return-path: Received: from order.stressinduktion.org ([87.106.68.36]:40155 "EHLO order.stressinduktion.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S966349Ab3HHUQa (ORCPT ); Thu, 8 Aug 2013 16:16:30 -0400 Content-Disposition: inline In-Reply-To: <20130808194702.GH14001@order.stressinduktion.org> Sender: netdev-owner@vger.kernel.org List-ID: On Thu, Aug 08, 2013 at 09:47:02PM +0200, Hannes Frederic Sowa wrote: > On Thu, Aug 08, 2013 at 02:45:40PM -0400, Debabrata Banerjee wrote: > > On Wed, Jan 30, 2013 at 3:26 AM, Jiri Pirko wrote: > > > From: Marcelo Ricardo Leitner > > > > > > They will be created at output, if ever needed. This avoids creating > > > empty neighbor entries when TPROXYing/Forwarding packets for addresses > > > that are not even directly reachable. > > > > > > Note that IPv4 already handles it this way. No neighbor entries are > > > created for local input. > > > > > > Tested by myself and customer. > > > > > > Signed-off-by: Jiri Pirko > > > Signed-off-by: Marcelo Ricardo Leitner > > > --- > > > net/ipv6/route.c | 2 +- > > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > > > diff --git a/net/ipv6/route.c b/net/ipv6/route.c > > > index e229a3b..363d8b7 100644 > > > --- a/net/ipv6/route.c > > > +++ b/net/ipv6/route.c > > > @@ -928,7 +928,7 @@ restart: > > > dst_hold(&rt->dst); > > > read_unlock_bh(&table->tb6_lock); > > > > > > - if (!rt->n && !(rt->rt6i_flags & RTF_NONEXTHOP)) > > > + if (!rt->n && !(rt->rt6i_flags & (RTF_NONEXTHOP | RTF_LOCAL))) > > > nrt = rt6_alloc_cow(rt, &fl6->daddr, &fl6->saddr); > > > else if (!(rt->dst.flags & DST_HOST)) > > > nrt = rt6_alloc_clone(rt, &fl6->daddr); > > > > > > > > I'm not sure this patch is doing the right thing. It seems to break > > IPv6 loopback functionality, it is no longer equivalent to IPv4, as > > stated above. It doesn't just stop neighbor creation but it stops > > cached route creation. Seems like a scary change for a stable tree. > > See below: > > > > $ ip -4 route show local > > local 127.0.0.0/8 dev lo proto kernel scope host src 127.0.0.1 > > > > This local route enables us to use the whole loopback network, any > > address inside 127.0.0.0/8 will work. > > > > $ ping -c1 127.0.0.9 > > PING 127.0.0.9 (127.0.0.9) 56(84) bytes of data. > > 64 bytes from 127.0.0.9: icmp_seq=1 ttl=64 time=0.012 ms > > > > --- 127.0.0.9 ping statistics --- > > 1 packets transmitted, 1 received, 0% packet loss, time 0ms > > rtt min/avg/max/mdev = 0.012/0.012/0.012/0.000 ms > > > > This also used to work equivalently for IPv6 local loopback routes: > > > > $ ip -6 route add local 2001:::/64 dev lo > > $ ping6 -c1 2001::9 > > PING 2001::9(2001::9) 56 data bytes > > 64 bytes from 2001::9: icmp_seq=1 ttl=64 time=0.010 ms > > > > --- 2001::9 ping statistics --- > > 1 packets transmitted, 1 received, 0% packet loss, time 0ms > > rtt min/avg/max/mdev = 0.010/0.010/0.010/0.000 ms > > > > However with this patch, this is very broken: > > > > $ ip -6 route add local 2001::/64 dev lo > > $ ping6 -c1 2001::9 > > PING 2001::9(2001::9) 56 data bytes > > ping: sendmsg: Invalid argument > > I do think that the patch above is fine. I wonder why you get a blackhole > route back here. Maybe backtracking in ip6_pol_route or in fib6_lookup_1 was > way too aggressive? Ah sorry, before rt->n removal everything worked a bit different. rt6_alloc_cow did fill rt->n back then. To fix both things we would have to bind a neighbour towards the loopback interface into the non-cloned rt6_info if it feeds packets towards lo. Pretty big change for old stable kernels, I guess. :/ Marcelo, any idea how to deal with this? My guess would be a revert, but I don't know the impact on the tproxy issue. Greetings, Hannes