Re: [patch net] ipv6: do not create neighbor entries for local delivery

From: Hannes Frederic Sowa <hannes@stressinduktion.org>
To: Marcelo Ricardo Leitner <mleitner@redhat.com>
Cc: Debabrata Banerjee <dbavatar@gmail.com>,
	Jiri Pirko <jiri@resnulli.us>,
	"davem@davemloft.net" <davem@davemloft.net>,
	"netdev@vger.kernel.org" <netdev@vger.kernel.org>,
	Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>,
	"jmorris@namei.org" <jmorris@namei.org>,
	"yoshfuji@linux-ipv6.org" <yoshfuji@linux-ipv6.org>,
	Patrick McHardy <kaber@trash.net>,
	"Banerjee, Debabrata" <dbanerje@akamai.com>,
	Joshua Hunt <johunt@akamai.com>
Subject: Re: [patch net] ipv6: do not create neighbor entries for local delivery
Date: Thu, 8 Aug 2013 21:06:24 +0200	[thread overview]
Message-ID: <20130808190624.GF14001@order.stressinduktion.org> (raw)
In-Reply-To: <5203EB4C.5020905@redhat.com>

On Thu, Aug 08, 2013 at 04:02:36PM -0300, Marcelo Ricardo Leitner wrote:
> Em 08-08-2013 16:01, Hannes Frederic Sowa escreveu:
> >On Thu, Aug 08, 2013 at 02:45:40PM -0400, Debabrata Banerjee wrote:
> >>On Wed, Jan 30, 2013 at 3:26 AM, Jiri Pirko <jiri@resnulli.us> wrote:
> >>>From: Marcelo Ricardo Leitner <mleitner@redhat.com>
> >>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
> >>
> >>--- 2001::9 ping statistics ---
> >>1 packets transmitted, 0 received, 100% packet loss, time 0ms
> >
> >Which kernel version are you using? Perhaps you miss another fix? It works 
> >for
> >me. Also I cannot find this patch in net-next?
> 
> It wasn't needed/applied as the route cache was removed.

Do you mean the rt->n(eighbour) removal? There was no removal of a route cache
in IPv6 land. The cache is merely in the routing table itself.

Greetings,

  Hannes