Re: IPv6 default route flapping

[Joerg Sonnenberger <joerg%bec.de@localhost>]

On Tue, Apr 20, 2021 at 10:09:47AM -0400, Jan Schaumann wrote:
> Greg Troxel <gdt%lexort.com@localhost> wrote:
> > 
> > Jan Schaumann <jschauma%netmeister.org@localhost> writes:
> > 
> > > Apr 20 01:32:32 netbsd dhcpcd[17397]: xennet0: soliciting an IPv6 router
> > > Apr 20 01:32:34 netbsd dhcpcd[17397]: xennet0: Router Advertisement from fe80::caa:49ff:feaf:1815
> > > Apr 20 01:32:35 netbsd dhcpcd[17397]: xennet0: fe80::caa:49ff:feaf:1815 is unreachable
> > > Apr 20 01:32:35 netbsd dhcpcd[17397]: xennet0: soliciting an IPv6 router
> > > Apr 20 01:32:44 netbsd dhcpcd[17397]: xennet0: fe80::caa:49ff:feaf:1815 is reachable again
> > > Apr 20 01:32:52 netbsd dhcpcd[17397]: xennet0: fe80::caa:49ff:feaf:1815 is unreachable
> > > Apr 20 01:32:52 netbsd dhcpcd[17397]: xennet0: soliciting an IPv6 router
> > > Apr 20 01:32:54 netbsd dhcpcd[17397]: xennet0: Router Advertisement from fe80::caa:49ff:feaf:1815
> > > Apr 20 01:32:55 netbsd dhcpcd[17397]: xennet0: fe80::caa:49ff:feaf:1815 is unreachable
> > > Apr 20 01:32:56 netbsd dhcpcd[17397]: xennet0: soliciting an IPv6 router
> > 
> > I don't know what's wrong, but obviously you should 'tcpdump -w IPV6
> > ip6' and look at it.
> 
> That's unfortunately not very revealing, as it merely
> shows the neighbor solicitations and router advertisements:

In the cases we had before, it was always two advertisements short after
each other. The first one declared the router to no longer be active and
the second declared it to be alive again. I forgot which of the timer
fields was the mark for that.

I was wondering about adding a hackish workaround for such misconfigured
routers so that the first event is not processed for a second or two and
ignored if it is cancelled within that window.

Joerg