On 03/28/2018 08:36 AM, Tom Eastep wrote:
> On 03/28/2018 03:30 AM, Brian J. Murrell wrote:
>> On Tue, 2018-03-27 at 12:44 -0700, Tom Eastep wrote:
>>>
>>> I've asked the maintainer of Foobar Linux, a RHEL-based distribution,
>>> for details. He found a neighbor discovery cleanup patch from way
>>> back
>>> in 2014 that solved the problem for him.
>>
>> Do we have a copy of this patch or know where it is hiding?
> 
> I don't have it currently, although I am attempting to identify it.
> 

There was a major change to the Linux IPv6 stack in the 4.2 kernel
release. Prior to that time, all successful route lookups were cached in
the IPv6 routing table (which is a Radix Trie). Beginning with 4.2, such
entries are only created when there is PMTU exception to the address.
The RHEL 7.5 kernel includes this change set.

When this type of problem occurred on a pre-4.2 kernel, 'ip -6 route
flush cache' would eliminate it for a bit. It was on a 3.17.x kernel
that I saw the problem. You are running a 4.4.x kernel, so the 2014 fix
isn't applicable. Udo is also running a 4.4 kernel.

I'm not seeing the problem with my 4.9.0 kernel and I haven't had any
workarounds in place since I installed that kernel as part of my upgrade
from Debian 8 to Debian 9.

I'll take a look at the kernel changes between 4.4 and 4.9 to see if I
can identify anything. If you forward me the output of 'shorewall6
dump', I'll see if I can spot anything there as well.

-Tom
-- 
Tom Eastep        \   Q: What do you get when you cross a mobster with
Shoreline,         \     an international standard?
Washington, USA     \ A: Someone who makes you an offer you can't
http://shorewall.org \   understand
                      \_______________________________________________

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