Subject: Re: [RRG] Renumbering...

From: Eliot Lear <[email-masked]>
Date: Mon, 25 Aug 2008 23:04:55 +0200

Hi Scott,

Scott Brim wrote:
> I'm going to reply to this whole thread in one message.
>
> To start with, what is a "mapping provider"?  There are three different
> functions that seem to be getting conflated:
>
>    a. EID prefix allocation (assuming we mean LISP)
>    b. advertisement of where to find a mapping (aka mapping "indexing")
>    c. providing/getting a mapping (for example the ALT)
>
> Based on some previous discussion, I think when you say "mapping
> provider" you mean (b), indexing, i.e. advertisement of where to obtain
> a mapping for a prefix.  However, I am not sure, since other parts of
> this thread seem to combine that with prefix allocation.
>    

A perfectly reasonable answer to your question is, (d) all of the above ;-)

>> It's not so clear.  It depends on where aggregation occurs.  Also, keep
>> in mind that the primary function of a mapping provider is to provide a
>> stable EID prefix, so this sort of change should be extremely rare!!
>>      
>
> "provide a stable EID prefix" ... Which definition of "mapping provider"
> is this?  The original allocator of the prefix (my (a) above)?
>    

Using your functional breakdown above, (b+c).  However, (b+c) is 
necessarily tied to (a) at some point because ALT relies on aggregation 
to scale.  I am not saying that this needs to occur at the first level 
of the topology, or perhaps even at the 2nd, but that it is something 
that should be studied and may change over time with operational experience.
> Tony: There is no reason why there should be a single ALT aggregator
> node responsible for a prefix, and good reasons why there should be
> more.  There would be at least two, or more, for redundancy.  A site
> would connect to all, and all would advertise an aggregated prefix
> including the site's prefix, further into the ALT.
>    

Whoever advertises a prefix should best maintain consistent policies.  
Otherwise weird things can happen.  For instance, if the prefix is 
disaggregated in some way, longest match first would shift traffic.  If 
payment models are tied to traffic, routing tables would explode.  So 
let's say that would be one policy that the *owner* of a prefix may wish 
to impose.  Is the owner IANA, an RIR, or one of these top level 
aggregators?  Or is it the end user?

> ALT aggregators are "clustered" in the sense that they connect to other ALT
> nodes that are responsible for longer or shorter prefixes in their
> branch of the ALT tree.  Geography has nothing to do with it.

I mentioned geographic independence because at different times ALT 
configuration proposals have arisen that are not geographically 
independent.  I think that would be a mistake.  But see below.

> On the
> other hand it is extremely likely that prefix allocation will (continue
> to be) on a regional basis, as the RIRs are today, in which case the ALT
> aggregators for a particular prefix could easily all be in the same region.
>    

I agree it is possible, which is why I wrote that I believe this is an 
area for further study.  At some point we leave the realm of technical 
and enter the realm of business and political.  ALT providers at the top 
level will advertise aggregates, to be sure.  Those aggregates need to 
be allocated from someone, to be sure.  If an ALT provider can be other 
than an RIR with the RIRs still existing as a function, then perhaps 
that is the ultimate case where your (a) and (b+c) above are split, 
where this non-RIR then has to either fulfill the role of an RIR by 
providing allocations to the layers below, or has to arrange with the 
appropriate RIRs that the appropriate allocations are made based on 
provider.

Eliot