Re: Generic anycast addresses...

On Thu, 30 May 2019 at 10:58, Toerless Eckert <tte@cs.fau.de> wrote:
>
> I cant brainstorm a lot more without more details of what you're
> trying to achieve, and  therefore what the constraints are.
>
> Worst case, you float the idea to a single ULA prefix defined
> by your RFCs mecanism and see how reviewers like this. At least its
> a lot better than trying to define a "well known" rfc1918
> anycast address - because your application defined ULA
> prefix has a very low probability of colliding with somebodies
> actually used ULA prefix.

Per RFC4193 4.1 and the route propagation constraint, ULAs effectively
have an organisation scope by default. That may be too small or too
large for other anycast use cases.

If there is a reserved well-known ULA prefix, then RFC 4193 would have
to be updated to exclude that value from the algorithm. We also don't
know if the chosen well-known ULA prefix is already in use somewhere.

I think a better idea is a formal class of anycast addresses with fine
grained scopes that match (or are) the multicast address scopes.

"IPv6 Formal Anycast Addresses and Functional Anycast Addresses"
https://tools.ietf.org/html/draft-smith-6man-form-func-anycast-addresses-00

> On Wed, May 29, 2019 at 05:41:04PM -0700, Ted Lemon wrote:
> > Indeed, the propagation pattern of a ULA would work nicely for this, but there???s no way to do this automatically.   I might have (and indeed unfortunately it???s common to have) more than one ULA on a constrained network.   How do I pick?   :)
> >
> > So what I really want is indeed something that is treated like a ULA, but that can be a constant, and not something that has to be derived.
>
> --
> ---
> tte@cs.fau.de
>
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