Subject: RE: Comments on draft-ietf-iptel-glp-00.txt

From: Matt Squire <[email-masked]>
Date: Mon, 08 Mar 1999 14:59:44 -0500

At 08:27 AM 3/8/99 -0500, David R. Oran wrote:
>> > - The ability to do fairly strightforward route aggregation
>> (of course
>> > modulo the problems of multiple metrics and the lack of a
>> totaly order
>> > among them).
>>
>> Actually even with prefixes, it seems hard. Basically - are
>> the prefixes
>> expressed in terms of bits, or in terms of decimal numbers. Decimal is
>> more logical, but then to aggregate to +1-555, you must collect
>> +1-555-1, +1-555-2, +1-555-3, etc., which is 10 routes. If its done
>> bitwise, it only requires 2.
>>
>> Thoughts?
>>

Planning for general aggregation is probably wasteful.  I'm in area code
919 in North Carolina.  Area code 920 is in Wisconsin, and 918 is in
Oklahoma.  I don't see that I'd be aggregating these together unless I'm
aggregating all +1 numbers together.  I don't predict many prefixes of the
form +1-9 or +1-91 being of any use, nor do I think many like +1-919-9 are
of great value.  Writing code that goes and checks for possible aggregation
at arbitrary bit/byte boundaries seems like a waste of time.  Phone numbers
are heirachical and based on groups of digits, we should plan for
aggregation along the same lines.  

So I don't think we should worry about how to make aggregation easier when
we choose representations, we should optimize representations for processing.

- Matt

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This message came from the IETF IPTEL Working Group Mailing List.

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From: "David R. Oran" <[email-masked]>
Date: Mon, 8 Mar 1999 15:19:45 -0500

The major reason I would argue for general aggregation is so that the
aggregator doesn't need to understand the semantics or assignment
politics of telephone numbers. We once had such an aggregation scheme in
the IP world (class-based addressing) and we didn't like where we wound
up.

Furthermore, semantics-blind aggregation is likely to wind up being
simpler to both implement and administer (IMHO). The performance is
likely to be as good or better as well, with data structures like
level-compressed tries and the like.

I'd make one exception to this principle. If there's a set of cases
where the aggregator can be told a purported "hole" in a set of
otherwise aggregatable prefixes isn't actually present somewhere, then
the aggregator can do a much better job of coalescing parts of the
address space. For example, if there's block of numbers like "+1-600"
which are known not to exist then telling the aggregator this will allow
for "+1-***" to be aggregated when otherwise it would be missed due to
the hole.

Dave.

> -----Original Message-----
> From: Matt Squire [mailto:[email-masked]]
> Sent: Monday, March 08, 1999 3:00 PM
> To: David R. Oran; Jonathan Rosenberg
> Cc: Scott Petrack; Alok Mittal; iptel
> Subject: RE: Comments on draft-ietf-iptel-glp-00.txt
>
>

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From: Jonathan Rosenberg <[email-masked]>
Date: Tue, 09 Mar 1999 19:06:45 -0500

> for "+1-***" to be aggregated when otherwise it would be missed due to

I agree that semantic blind aggregation is a better idea. Otherwise,
each poor LS needs to know the structure of the numbers everywhere in
the world. 

This hole idea is interesting. Would you also send the hole along with
the aggregated prefix? If not, an LS is right back to needing to know
about the structure of number allocations in order to aggregate. If
there is an inconsistency in the views of two LS's, you could have some
interesting mis-routing problems.

-Jonathan R.

-- 
Jonathan D. Rosenberg                       Lucent Technologies
Member of Technical Staff                   101 Crawfords Corner Rd.
High Speed Networks Research                Holmdel, NJ 07733
FAX: (732) 834-5379                         Rm. 4C-526
EMAIL: [email-masked]
URL: http://www.cs.columbia.edu/~jdrosen

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From: "David R. Oran" <[email-masked]>
Date: Wed, 10 Mar 1999 02:01:56 -0500

> From: Jonathan Rosenberg [mailto:[email-masked]]
> Sent: Tuesday, March 09, 1999 7:07 PM
> To: David R. Oran
> Cc: Matt Squire; Scott Petrack; Alok Mittal; iptel
> Subject: Re: Comments on draft-ietf-iptel-glp-00.txt
>
>
> David R. Oran wrote:
> >
I'm beginning to feel like I'm living inside a Beatles song - "...fixing
a hole where the rain gets in, to stop my mind from wandering"... now
where was I...

...oh yes. Well I hadn't actually thought of the idea of propagating
"hole advertisements". I was thinking of simply making an assertion to
the aggregator via some local configuration. I don't see how this
necessarily leads to the LS (remind me what the acronym stands for - I'm
typing this at 2AM...) having to know the structure of allocations? Just
like you have to know whether you can reach prefix "+44 365" in order to
inject a route to "+44 365" you likewise have to know that all routes to
"+777" lead to a black hole. If this is what you mean by knowing the
structure of allocations, then yes, but this isn't global knowledge
needed by every LS, only those LSs serving gateways advertising routes
to prefixes "surrounding" the hole.

It may be feasible to actually inject the route to the hole, but this
begs the question of which LS(s) actually do it and whether it looks
like a route to a black hole or is something special. In any event, I
threw out the idea without a whole lot of thought behind it, and now
that you've called my bluff I'll have to go off and see exactly what the
further implications are.

Dave.

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