Re: Geographic v. topological address allocation

[Vadim Antonov <avg () pluris com>]

Sean Doran wrote:
 
> As tli pointed out the top of the hierarchy is not
> arbitrary, it must be default free.

Sorry for the nitpicking, but this definition has at least two
flaws:

a) there's a bi-partite backbone configuration, where each half
   has default pointing to the other half.  Both do not have to
   carry full routes.  (Of course, this scheme has problems with
   packets destined to the blue, or can be extended to more than
   two partitions).

   Actually, there's a very simple way to fix the problem with
   packets to nowhere.  Simply have routers at exchange points to
   drop packets routed back to the interface from which they came
   from.

b) multihomed non-transit networks may want to be default-free
   and carry full routing to improve load sharing of outgoing
   traffic.  Since they are non-transit, they cannot be considered
   "top of hierarchy".
 
> Consequently, the number of things in the top,
> default-free hierarchy is always going to be limited, no
> matter what "type" of hierarchical allocation scheme is
> proposed.

Bingo.  Faster boxes, anyone? :)
 
> The further requirement that any given area be fully
> contiguous means that the "top" of the hierarchy must be
> self-repairing.

Note that IXPs are not "top" of the hierarchy, but just 
aggregators for essentially point-to-point links between
tier-1 backbones.

> One could propose to implement this as a big bridged
> network.  The original DGIX proposal was along these
> lines.  Operational experience with much smaller but still
> big bridged exchange points has demonstrated pretty much
> conclusively that this is a Really Really Bad Idea.

Not only technically -- politically that was a suicide,
as it assumed a signle operator (consortium, or pork money
funded).
 
--vadim