IPv6 broken on Fedora 20?

[Hannes Frederic Sowa]

On Thu, Dec 19, 2013 at 06:59:56PM +0100, Tore Anderson wrote:
> * Hannes Frederic Sowa
> 
> > The kernel should install the IPv6 address with /64 prefixlen without also
> > installing a prefix route for that subnet. Currently the kernel does this
> > automatically.
> 
> I don't think you can do that from user-space. If you add a /64 (any >
> /128 really), you automatically get a on-link route too. At least I
> cannot spot how to do it in ip-address(8). So the only way to deal with
> the L=0 case when doing RA-processing in user-space is to add the
> address as a /128.

Since the current kernel has extended ifa_flags to 32 bit it is now very
straightforward and easy to add such functionality (this was done for
NM correctly supporting privacy addresses). I already had this on my
todo list for some time but did not get to it.

I still have to review how address and prefix route deletion should happen if
this feature gets introduced.

> Once you're doing that, it's probably easier to handle L=1 by simply
> adding the on-link route directly, rather than adding the address as a
> /64 and relying on the kernel to add the route for you. The two should
> result in the same functionality, though, so I'm don't really understand
> what's actually broken here.

I guess it breaks generation of privacy addresses.

But you are right, essentially it should work but some assumptions were
made in the kernel which should have been checked first.

Greetings,

  Hannes