Re: Allocation of a Global Prefix (Re: I-D Action: draft-ietf-6man-sids-01.txt)

[Ted Hardie <[e-mail]>]

Hi Bob,

On Wed, May 18, 2022 at 5:29 PM Bob Hinden <[e-mail]> wrote:

> Suresh,
>
> In Section 5.  Allocation of a Global Unicast Prefix for SIDs the draft
> discussed the use of a dedicated prefix for SR domains.   I think that is
> an interesting idea, however it then says:
>
>    The SRv6 operational community, which is the first intended user of
>    this block, is requested to come up with conventions and guidelines
>    for the use of this newly allocated address block in line with their
>    requirements.
>
> I think the notion of doing the allocation first and then come up with
> conventions and guidelines for how to use it is problematic.   I think it
> needs to be the other way around, as well as probably combining it with the
> IANA request for a prefix.
>
>
The converse problem, of course, is that if you try to create conventions
and guidelines before you have any allocation you may end up with
significant aspects of the deployed reality that aren't reflected.  At
least in my experience, operational reality tends to throw some curveballs
at you that didn't occur in labs or simulations.

I think the major point here is to allow SIDs traffic to be easily
distinguished from other traffic; any allocation gets that done.  So the
first guideline might be "use this prefix when that need is present".  I
think any other guidelines need to be almost at that same level of
generality at this stage, and that we'll see detailed conventions and best
practices emerge after there is more experience.

I have also been wondering if ULAs could be used for this purpose.   I
> think they have most of the right properties, that is, not intended for
> global routing and easily filtered at administrative boundaries.   An SR
> domain could allocate one or more ULA prefixes. Or it might be time to
> define the centrally allocated ULA-C part of the ULA space.
>

Since there are non-SIDs ULAs, I think using the currently defined space
misses the primary goal of distinguishing the usage type, or at least makes
it harder to achieve.

I don't think setting up a new central registry is a goal here.   While
ULA-C space could be redefined as not requiring a central registry, I
believe it is simpler to use new space and define what principles govern it
rather than redefining something that was set aside for a different
purpose.

Just my take on it,  of course,

Ted Hardie