Subject: Re: [RRG] Micronet & MAB terminology

From: Robin Whittle <[email-masked]>
Date: Wed, 05 Dec 2007 11:21:41 +1100

Hi Scott,

Regarding my suggested terminology, you wrote in the thread
"Thoughts on the RRG/Routing Space Problem" (msg 713):

>> The MAB, UAB and micronet terminology I use here is discussed
>> in:  http://psg.com/lists/rrg/2007/msg00533.html
>>      http://psg.com/lists/rrg/2007/msg00535.html
>
> iirc a MAB is an aggregate of addresses that are not globally
> routed,

"Mapped Address Blocks" are not globally routed (advertised in BGP)
in eFIT-APT or the original conception of LISP, but they are in Ivip
and for whichever MABs are handled by LISP Proxy Tunnel Routers.

> a "micronet" is a chunk of addresses within that, which need not
> be on a power-of-2 boundary, and a UAB is somewhere in the
> middle.

Yes.  A User Address Block is a range of addresses one end-user
controls the mapping of.  They can configure this as one micronet or
as many micronets as they like, subject to the technical
restrictions of the ITR-ETR scheme (AKA map&encap scheme).

For MAB, I think it's just as easy to say what you mean.

By all means do so.  I think it is a common enough concept in all
these ITR-ETR schemes that it deserves a term which saves space and
can clearly be seen as meaning one thing.  The troubles with people
making up a phrase to describe something in their own way, such as:

  ... prefix which is not routed and for which the mapping
  database has entries ...

  ... address block which is excised from the DFZ and for which
  ITRs tunnel packets when addressed thereto ...

  ... prefix which is advertised by all ITRs and for which the
  mapping database controls the ITR's encapsulation of packets
  whose destination addresses fall within this prefix ...

  etc.

is firstly that it is tedious and wordy, and secondly that there is
a high risk that even specialists in this field won't understand
that all three phrases above refer to the same thing, with the
exception that the MAB described in the third one is advertised and
the first two are not.

Hopefully other people will find MAB and the other terms useful, or
suggest some alternatives.  I believe we do need some common
terminology to make our discussions understandable, even to
ourselves - let alone hapless newcomers to this difficult field.

I am keen to keep the definitions wide enough to not constrain the
technical details of each ITR-ETR / map&encaps scheme, while still
making the terms useful.

> For "UAB" and "micronet", we have tried non-power-of-2 alignment
> in the past and it has been a big problem.  We ended up with CIDR
> on power-of-2 boundaries for a good reason.

That's fine, but Ivip is intended to have arbitrary boundaries and
lengths regarding the UAB and micronet, so I don't want to use
terminology which assumes power-of-2 boundaries.

> The term for a chunk of addresses aligned on a power-of-2 boundary
> is a prefix.  We've been using this for over 20 years.

That's fine, but I can't use this for Ivip's UAB or micronet
concepts.  If you use the term "prefix", you have to attach further
words to describe exactly what sort of prefix you mean, which raises
the problems of multiple complex and confusing ways of describing
the same things.

> Finally, the labels "M" and "U" unnecessarily assume a simple
> two-tier system.

Still, I think they are useful.  Others may find them useful too.
If a scheme uses a more complex hierarchy of address divisions, then
the terms won't work for that, and new terms or phrases should be used.

 - Robin

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