[Dnsmasq-discuss] Cannot assign IPv6 address for /96 subnet

Dan Williams dcbw at redhat.com
Sun Mar 3 16:05:37 GMT 2013


On Fri, 2013-03-01 at 16:58 -0500, Pavel Simerda wrote:
> ----- Original Message -----
> > From: "Joakim Langlet" <joakim.langlet at seaview.se>
> > 
> > Pavel and Dan,
> > Thank you for your answers. It makes it a lot easier for me to
> > understand the problems I have with Ubuntu 12.04 and also Debian
> > Wheezy RC-1 currently.
> 
> No problem, feel free to ask more questions.
> 
> > I use DHCPv6 for address assignment (nicely serviced by dnsmasq) and
> > radvd is used to announce the /96 networks. This all works. I get an
> > address and a /96 route, but unfortunately there is also an
> > additional route (/64) added.
> 
> Sounds wrong.
> 
> > This additional route screws up routing to other /96 networks (locally).
> 
> Are you sure? A /96 route should always take precedence over a /64 route, as it is more specific.
> 
> > I ask for your advice, should I consider this additional (bad) route
> > being a kernel bug or is it more likely something Debian specific?
> 
> If it is a kernel bug (and I don't think so), then the /64 route is a kernel-originated route and it will appear even without the DHCP client. If it only appears when you run DHCP client, it is most likely a bug in the DHCP client itself. If it appears when DHCP client is run by NetworkManager, it is more likely a bug in NetworkManager.

And if you're not running NetworkManager, then it's a bug in
dhclient-script, or whatever script you're using to apply the DHCP
configuration.  Again, by default dhclient tells the script to use
a /64, which is wrong.

Dan

> Also, kernel routes tend to have preferred life time and valid lifetime set (and different from each other).
> 
> > I am prepared to dig into the source to find it....
> > 
> > It seems like the additional route is added by *default*. It has the
> > same prefix as announced by the router, but cut down to /64.
> > 
> > I have a temporary fix for it. I simply look for it in the routing
> > table and delete the extra route using script, but it would be nice to
> > track down the real reason so that it gets solved.
> 
> Agreed.
> 
> > Again, thanks a lot for your answers on DHCPv6. It all makes much
> > more sense now.
> 
> Thanks for your interest.
> 
> Cheers,
> 
> Pavel





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