OSPF for IPv4 over IPv6 only?

[Ondrej Zajicek]

On Mon, Apr 01, 2024 at 04:14:51PM +0200, Sebastian Hahn wrote:
> > 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.

Hi

Unfortunately, RFC 5838 chose the worst way to represent IPv4 in
Link-LSA, so there is no reliable way to know whether received Link-LSA
should be interpreted as IPv4 or IPv6.

Although one could have option that forces it to interpret as IPv6, i
would prefer to have 'extended next hop' option that allows to accept
both IPv4 and IPv6 next hops in Link-LSA.

We could use heuristic, like if first u32 is fe800000, it is IPv6,
if remaining u32s are 0, it is IPv4, And hope that nobody uses both
fe80::0 and 254.128.0.0.

-- 
Elen sila lumenn' omentielvo

Ondrej 'Santiago' Zajicek (email: santiago at crfreenet.org)
"To err is human -- to blame it on a computer is even more so."