Re: Dealing with ICMPv6 network unreachable.

[Roy Marples <roy%marples.name@localhost>]

On Fri, 2015-04-03 at 22:02 +0100, Roy Marples wrote:
> On Sat, 2015-04-04 at 03:16 +0700, Robert Elz wrote:
> > I kind of agree with Greg Troxel, if there's any problem at all on the
> > NetBSD system, it would be in attempting to send to the global addr from
> > a LL addr - but even that isn't as clear cut as it seems, the global
> > addr might be on the local link, in which case the connection should succeed.
> 
> I agree on all points.
> 
> > I certainly believe your holiday apartment's router is broken though,
> > advertising itself as a router when it has no routes at all (beyond LL)
> > is just perverse.
> 
> My knee jerk reaction was the same.
> But after contemplating the issue while soaking the sun it's not really
> that broken. It's perfectly possible that the router is configured to
> request a Prefix Delegation from a upstream DHCP server which has gone
> silent. The normal operation of rtadvd(8) is to advertise itself as a
> router and any prefixes on the advertising interface - of which there
> will be none if Prefix Delegation has failed.
> 
> > For NetBSD, aside from the unlikely possibility of a magic new connect
> > syscall, about all you can do when facing a broken router like this, would be
> > to disable IPv6 (which admittedly right now is harder than it could be.)
> > 
> > Certainly "fixing" it to act (in any way at all) upon the ICMP is not
> > the right thing to do.
> 
> Roy
> 
> 
> Well, as discussed above, fixing it by not adding a default route if no
> global addresses are available isn't a good solution either (and one I
> have also considered).

I can't think of a better way of fixing it though!
And seeing as the current discussion isn't looking like any possible fix
for this is possible in NetBSD I've made dhcpcd skip adding a default
route for routers which advertise themselves as a router but without any
global prefixes. I've also added an option to turn this off and have the
original behavior.

http://roy.marples.name/projects/dhcpcd/ci/6ead1d4962b514e8?sbs=0

Roy