encoding link ID in link-local addrs (Re: about violation of standards)

[神明達哉 <[e-mail]>]

At Fri, 19 Apr 2019 07:00:01 +0000,
"Pascal Thubert (pthubert)" <[e-mail]> wrote:

> While I completely object with Alexandre’s argument I tend to agree with
the end goal.
>
> Some functions in the router are complex to implement because same value
for a link local address appears on multiple interfaces.

Yeah, I see that motivation.  The generic/usual answer of mine to that
kind of problem is to use the sockaddr_in6::sin6_scope_id (or anything
similar to it for a non-POSIX platform) and the extended textual
format for scoped addresses as described in RFC4007.  But I can
imagine there are cases where they are not enough and/or applicable.

So...

> It would be useful to be able to encode an abstract interface ID
somewhere in the /64. Legacy 00 would mean unspecified...

(As a co-author of RFC4007 I can't help correcting it to "link ID"
instead of "interface ID" but:-)... yes, I can imagine we might reach
some consensus of using some portion of the 128-bit space to encode
that information.  But, that will require a lot of considerations,
including

- whether the goal is really impossible to achieve with currently
  available tools
- especially if the first answer is something like "it can, but it's
  not convenient", then whether the goal really justifies to consume
  a particular space of the finite resource of address space
- whether it has to be inside the upper 64 bits (or in more general,
  inside the "subnet prefix" part).  If it has to be so, whether it
  has to be within the first 32 bits (if not, at least it doesn't
  conflict with the BSD implementation).
- if, like draft-petrescu-6man-ll-prefix-len suggests, the encoded ID
  is the same for all nodes in the link, how we assign those IDs and
  how we ensure their uniqueness, how each node knows the ID on
  generating addresses, etc.

When I said "I'm open to discussion", I meant I'm willing to discuss
these matters.  Of course, since there are so many open questions, I'd
expect it to take quite a long time, and I can't say at this point
whether I support the eventual proposal that the WG might come up
with, or whether we can really expect any WG-wide consensus.  I'm now
clarifying the intent, as it didn't seem to be clear enough.

--
JINMEI, Tatuya