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

[Alexandre Petrescu <[e-mail]>]

Le 19/04/2019 à 18:25, 神明達哉 a écrit :
> At Fri, 19 Apr 2019 07:00:01 +0000,
> "Pascal Thubert (pthubert)" <[e-mail] 
> <mailto:[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.

In my case, it  is a human sysadmin (myself) that assigns those IDs (the
IID and the ID in fe80:1::/32) and I ensure the uniqueness.

I think it is common practice to have sysadmins to ensure uniqueness;
this is what I also do with some of the /56s assigned to me for GUAs.  I
make a plan, get agreement, document it and share it with the interested
parties in my setting.  I also teach every new comer this addressing
archi for a while, then I stop, because the plans are there.

I am not sure I need to document that outside my setting.

Alex