Re: failed to set IPv6 default route

[Dan Williams <dcbw redhat com>]

On Mon, 2012-09-24 at 08:05 -0400, Gene Czarcinski wrote:
> On 09/23/2012 08:56 AM, Gene Czarcinski wrote:
> > I have been doing some work trying to improve IPv6 dhcp support in 
> > NetworkManager.  This has involved a lot of (virtual) testing. One 
> > thing I began to notice is a lot of the following message appearing in 
> > syslog:
> >
> > [nm-system.c:1121] nm_system_replace_default_ip6_route(): (p32p1): 
> > failed to set IPv6 default route: -7
> >
> > The only way I have been able to get an IPv6 default route set is to 
> > use manual configuration and specify a gateway.  Everything else seems 
> > to produce this message.
> >
> > OK, is this a bug or is there something about configuration I do not 
> > understand?
> >
> >
> My question concerning if this is a bug stands.
> 
> However, I have been playing around (marvelous what you can do with some 
> qemu/kvm/libvirt virtual guests when you do not care if things get 
> really screwed up).  I thried using NetworkManager (the applet) to set a 
> default route but nothing seemed to work except specifying the gateway 
> when manually configuring IPv6.
> 
> I finally googled what appears to be (sort of) an answer. enter 
> something like the following command line command:
> 
>      ip  -6  route  add  default  via <fill_IPv6_address_of_'router'>  
> dev  eth0

So that's essentially what NM is trying to do, actually, but NM is
trying to do it with netlink (which is what /sbin/ip uses too actually)
but apparently the netlink options we're adding aren't quite correct
here.  They unfortunately change periodically when kernel changes
happen.  -7 appears to be NLE_INVAL, which would indicate the kernel
doesn't think the route we gave it is valid.  We'd have to dig a bit
further down to figure out what that error actually is.

Last time I had to do this, I had to rebuild /sbin/ip and make it print
out the exact netlink packet it was sending to the kernel.  Then I had
NM print out its packet and compared the two.  If only there was an
easier way...

Dan

> With that, "ip -6 route' actually shows a good default and, even better, 
> stuff starts to work.
> 
> IPv6 does not have a way of specifying a default route with dhp6 but, 
> that does not mean that we can do something which will be "good enough" 
> until those great folks in the IETF get things worked out.
> 
> We need something in the applet so that we can specify a default and 
> then issue something like the above command.
> 
> Note:  I may be wrong and this can be done in the applet and set 
> correctly ... if so, some kind of doc or change to the applet is needed 
> to make this capability clear.
> 
> Sort-of OT question:  Why can't I specify additional name servers and 
> search domains if I select IPV6 dhcp?
> 
> Gene
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