Re: kern/52554: IPv6 connections not routing to default gateway

[Ryota Ozaki <ozaki-r%netbsd.org@localhost>]

On Tue, Oct 3, 2017 at 10:08 AM, Roy Bixler <rcbixler%nyx.net@localhost> wrote:
> On Mon, Oct 02, 2017 at 02:15:01PM +0000, Roy Bixler wrote:
>>  I asked the network admin. and he tells me that that IPv6 routers are
>>  advertising priorities and the router that works has the highest
>>  priority.  He says that it's an option that was put into the Linux
>>  kernel a few years ago.  The option, CONFIG_IPV6_ROUTER_PREF, quotes
>>  RFC4191 as a reference.  From looking at the dhcp client logs, I can
>>  see that it's getting advertisements from all of the routers and it
>>  just picks the first one (i.e. sets its default route according to it)
>>  and disregards the others.  I still wonder why this doesn't happen
>>  with NetBSD 7.1.
>
> I'm fairly convinced that the problem is with dhcpcd.  With NetBSD-8,
> I tried an experiment, which set ip6mode to autohost and pass the -4
> flag to dhcpcd.  I observed that the correct default router was
> applied more often.  If it wasn't, then I could do an "ndp -R" command
> one (or a few) time(s).  If it found the highest priority router
> first, then "ndp -H" was enough to correct the default IPv6 router.
> If some other IPv6 router was found first, then a router with higher
> preference will not change the routing table.  However, similar
> experiments I did with NetBSD 7.1 had the same result.
>
> The difference is that, with NetBSD 7.1, dhcpcd will obey the router's
> priority.  Even if a lower preference router advertises first and is
> made the default IPv6 router, dhcpcd will correct that later if the
> higher preference router advertises.  With NetBSD 8, dhcpcd strictly
> takes the first IPv6 router that advertises and makes that the
> default.  It will never update the default unless I manually do "ndp
> -R" once or a few times, the highest priority router happens to
> advertise first and then I do "ndp -H" to update the routing table.

Thank you for the in-depth investigations.
Let's summon the author of dhcpcd :)

Roy (Marples), do you have any ideas?

  ozaki-r