Geographic v. topological address allocation
Vadim Antonov
avg at pluris.com
Fri Nov 21 23:15:43 UTC 1997
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
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