[AusNOG] IPv6 Addressing

[Karl Auer]

Graham Maltby wrote:
> I am probably showing my complete lack of IPv6 knowledge here
> but can someone explain the logic or reasoning behind allocating
> 18,446,744,073,709,551,616 address to a point to point link? Or
> suggest some reading that might clarify that.

Michael Christie (micchris) top-posted in reply:
> I would suggest:
> 1) It makes your design simpler: /64 everywhere
> 2) There are 18,446,744,073,709,551,616 /64s available*

This discussion has been done to death in forums like NANOG and the IETF
6man list. There is a draft RFC[1] that relaxes the standard /64 for
point to point links. Current best practice, such as it is, is to
*allocate* a /64 to each such link, but *configure* a /126.

Why be concerned about point to point links anyway?[2] There is little
difference between a /64 for two nodes or a /64 for a million nodes -
the vast majority of the addresses are still "wasted" anyway. The
percentage of addresses in use is still zero, to about 14 decimal
places :-)

The argument here is basically that you should not be thinking about
addresses any more - just about subnets. There are *enough* addresses in
a /64, no matter what the purpose of your subnet.

When you buy (say) a set of steak knives, you do not concern yourself
with how many atoms comprise them; there will be *enough*. You just want
a certain number of knives. Likewise with IPv6; addresses are no longer
of interest - just subnets.

Regards, K.

[1] draft-ietf-6man-prefixlen-p2p-xx.txt

[2] There are actually technical reasons for preferring small
    subnets on router-to-router links as a special case; see
    the above draft.
-- 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Karl Auer (kauer at biplane.com.au)                   +61-2-64957160 (h)
http://www.biplane.com.au/kauer/                   +61-428-957160 (mob)

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