Re: [RRG] ALT's strong aggregation often leads to *very* long paths

[Robin Whittle <rw@firstpr.com.au>]

Hi Noel,

I am replying to your two messages, in which you wrote, in part, and
in a different order:

>> I had too much difficulty understanding how CONS would work
>> anyway.
>
> CONS is conceptually fairly simple; think DNS, but replace "DNS
> names" with "IDs" and "A/etc records" with "RLOCs". The fine
> details differ a fair amount, for a long list of reasons having
> to do with the operational environment and requirements, etc, but
> that's the broad-stroke picture.

I think that function of the entire CONS network, treating it as a
black box, was to look up a distributed global database and return
the answer.  In this respect, it resembles the DNS.

However the CONS network was a network of message passing devices,
not unlike routers.


>> I think CONS and ALT are driven by a common goal - to build a
>> new network of routers in which aggregation is achieved to a
>> very high degree.
>
> This doesn't match my understanding of CONS at all. CONS nodes
> are not routers, any more than nodes in the DNS hierarchy are
> routers. CONS is just a resolution hierarchy, just like DNS; at a
> very high level, the only difference between DNS and CONS is that
> DNS maps from DNS names to A/etc records, whereas CONS maps from
> IDs to RLOCs.

The CONS nodes (CARs and CDRs) were functioning as peer elements in
a message passing network, organised in a way which resembles a
network of routers.  I recall that the topology of their connections
was supposed to be organised according to the address ranges they
were responsible for.  Likewise the topology of connections between
ALT routers in the ALT network.

CONS involved new protocols and software.  The ALT network ferries
queries, initial traffic packets and perhaps responses back and
forth in a broadly similar way, without the need for new protocols
or software.

Regarding my critique and K. Sriram's diagram:

http://www.firstpr.com.au/ip/ivip/misc/strong-aggregation-k.sriram.png

> Looking at the picture, though, I am completely confused by this
> one too (in the sense of 'it has no relationship to how I thought
> things worked').
> 
> ITRs (and ETRs) are not routers (although they are colocated with
> routers in a single box), and they are not connected in a mesh.
> In other words, I would never expect to see a packet sent from
> one ITR to another. Ever.

I agree.  If you imagine a modified version of the diagram, with
"ITR2" to "ITR8" converted to "ALT router 2" to "ALT router 8", then
 I think there will be no difficulty seeing it as an example of how
a query or initial traffic packet is passed from ITR1 to ETR1 via
the ALT network.


> The aggregation hierarchy is only there for the *resolution*
> phase (like DNS); there is no hierarchy associated with the
> handling of user data packets.

Yes - except for the initial traffic packets the ITR sends on the
ALT network when it doesn't yet have mapping data for those packet's
destination EIDs.

 - Robin

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