Re: PI/metro/geo [Re: The state of IPv6 multihoming development]

[Masataka Ohta <mohta@necom830.hpcl.titech.ac.jp>]

Noel;

> You see *only* 100K destinations in DFZ routing tables because some large
> percentage of the informaion has *already* been hidden (through use of
> hierarchical information hiding, e.g. subnets, etc).

Agreed, strongly.

>     > From what I gather from other stuff that refers to this, the down side
>     > is a longer path.
> 
> The tradeoff between routing efficiency (i.e. path length) and routing
> overhead (i.e. storage/computation/messages) is central to large-scale routing.

Considering geographically large, such as intercontinental, subnets,
host route is, technically, the only way to minimize the shortest path.

However, practically, the minimization for inter-ISP traffic is
impossible, as we can not expect all ISPs use consistent routing
metric, not because there is no consistent metric (e.g. geographycal
distance is an internationally consistent metric) but because there
is no metric to be compatible with all the business models of various
ISPs, which is why BGP does not use any metric.

Many, if not all, ISPs are assuming ASes are local with mostly same
diameter and untimately relies on AS-path length, down side of which
is, of course, a longer path.

							Masataka Ohta