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

From: Marcelo Ricardo Leitner <[email-masked]>
Date: Thu, 08 Aug 2013 16:02:36 -0300

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 <[email-masked]> wrote:
>>> From: Marcelo Ricardo Leitner <[email-masked]>
>>>
>>> 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 <[email-masked]>
>>> Signed-off-by: Marcelo Ricardo Leitner <[email-masked]>
>>>
>>> [...]
>>
>> 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.

Regards,
Marcelo