Re: draft-ietf-v6ops-addcon-03.txt ... ULAs of shorter-than-/48 and ULA multicast scope matching ...

[Tim Chown <tjc@ecs.soton.ac.uk>]

On Tue, Mar 13, 2007 at 07:30:51PM +1030, Mark Smith wrote:
> 
> I'm slightly confused be this, and I think the comment about not
> being able to summarise 16 /48 ULAs is what is confusing me.
> Summarisation seems to me to only be useful if you are going to
> announce a summary to an upstream entity of some sort, and is really
> only for the benefit of the upstream entity (e.g. upstream ISP, IGP
> backbone area, other areas carrying inter-area routes rather than a
> default etc.), as it reduces their route table and other routing
> resource requirements.
> 
> As ULAs are kept within private entity, and therefore there isn't any
> upstream entity, is there really any need to summarise to less than
> 16 /48 ULAs (in your scenario, for example)? If, within your
> organisation, your routers can't cope with 16 /48 ULAs, I'd think you
> problably have bigger routing problems to deal with (and a default
> route only might be a main (and only) solution to that)!

Well, were we talking of maybe a /36 rather than a /34, with aggregated
internal routing for sites within the prefix, then I think the above
approach could be useful.

> If you were summarising ULAs internally to scale an IGP by dividing the
> IGP into areas, would 16 areas, corresponding to the 16 /48s (global
> and ULAs), be too many to cope with ? I'm not really sure they would.

Well, think a little bigger than a /44 example?   What would you say then?

> I do see the operational benefits of having the /44 to /64 bits in the
> global and ULA addresses match. I'm not quite sure I see how
> summarisation by itself, which is how I read your paragraph, would be a
> justification to do that, when the consequences are increased chances
> of collision, should you join your /44 ULA domain with somebody else's.
 
Aligning the bits in the global and ULA addressing plan may have advantages
as you say.   That's the other aspect.

My personal concern is that network admins will pick all zeroes for the
ULA prefix, because they would rather have easy to type addresses than
a potential benefit for leakage/merger/etc.

> Have I somehow misunderstood what you're trying to get at?

No, your question is a good one, and we need some discussion :)

-- 
Tim