OSPF for IPv4 over IPv6 only?

[Sebastian Hahn]

Hi Pim,

> On 31. Mar 2024, at 11:04, Pim van Pelt <pim at ipng.nl> wrote:
> 
> Hoi Ondrej, Nico, Sebastian,
> 
> I am revisiting this thread based on the question from Benoit this week (https://www.mail-archive.com/bird-users@network.cz/msg07961.html).
> 
> On Tue, Jan 30, 2024 at 12:20:41PM +0100, Sebastian Hahn wrote:
> > > On 30. Jan 2024, at 10:32, Nico Schottelius via Bird-users <bird-users at network.cz> wrote:
> > > Is there a way to purely go IPv6 only and still relay stub network IPv4
> > > information via an IPv6 only internal area?
> > 
> > I was facing the same issue before, and unfortunately, RFC 5838
> > explicitly forbids IPv4 over IPv6 for OSPF.
> Sebastian - my interpretation of 5838 is slightly different, and I don't think it expressly forbids xAF nexthops:
> > 2.5: Although IPv6 link local addresses could be used as next hops for IPv4 address families, it is desirable to have IPv4 next-hop addresses.

My understanding came from this:

> In order to achieve this, the link's IPv4 address will be advertised
> in the "link local address" field of the IPv4 instance's Link-LSA.
> This address is placed in the first 32 bits of the "link local
> address" field and is used for IPv4 next-hop calculations. The
> remaining bits MUST be set to zero.

which to me reads like the statement about desirability just explains
why the technical design doesn't allow IPv6 next hops. I would be
happy to be wrong here.

Thanks
Sebastian