[ppml] Proposed Policy: IPv6 HD ratio

Geoff Huston gih at apnic.net
Tue May 10 16:29:26 EDT 2005

>One of the critical factors in efficiency is the depth of the network 
>hierarchy.  For a cable system provider, the depth may be shallow, making 
>it easy to fill up a stretch of addresses.  For someone that is a wide 
>area backbone provider, filling up the same stretch of addresses with 
>hosts is harder.
>Question 1 - does the HD ratio inherently account for this? Regardless of 
>the HD value that is.  It's a log ratio...so maybe yes. If so, maybe it's 
>just a question of what setting to use.

You can map a particular HD ratio setting to the concept of a network that 
achieves a fixed efficiency setting at each level of internal hierarchy, 
and adds an additional level of hierarchy each time the network by a factor 
of n (for some value of n)

An HD ratio of 0.94 corresponds to a 75% efficiency at each internal level 
of hierarchy, with a new level of hierarchy added when the network expands 
by a factor of 32

An HD ratio of 0.8 corresponds to a 70% efficiency at each level with a new 
level of hierarchy added each time the networks grows by a factor of 8.


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