[ppml] IPv6 Assignment Guidelines, Straw Man #2

michael.dillon at bt.com michael.dillon at bt.com
Tue Aug 21 05:15:11 EDT 2007

> As for whether /48 is the right choice or not, I honestly do 
> not know. I certainly do not see any reason to increase it. 
> How many end users on the planet could justify a /47?

As far as I can see there are only two types of end user that can
justify a /47. The first type is a large campus-type facility with lots
of network infrastructure, for instance a large military base or
Microsoft's central campus in the Seattle area. The second type is the
large corporation with many, many scattered geographical locations which
wishes to maintain tight control over Internet access by providing a
single Internet gateway and connecting their locations using a VPN. 

There just aren't very many large campus-type facilities around that
won't fit into a /48. They need to have a larger than usual internal
usage of networks. And large corporations will think very careful before
taking on the scaling challenges of a single Internet gateway combined
with the introduction of a new Internet protocol. The same
infrastructure that is used to hookup the locations to the VPN can be
used for IPv6 Internet access and issues of control can be dealt with
using smaller local IPv6 firewalls which removes the need to deal with
scaling issues. In that case, each location will get its own /48 and
their network architects can design a handful of site templates based on
a /48 subnetting scheme.

The ability to evade scaling issues and at the same time standardize
network designs will be a big motivator for larger corporates to NOT
chase /47 allocations but to just accept the local ISP's /48
allocations. Also, since IPv6 allows for multiple addresses per site,
they are not stuck with just accepting random ISP assignments. They can
also overlay this with central corporate addresses for important devices
such as firewalls, servers, etc. and they can still have a VPN as well.
This allows doing things like configuring all mail server (or mail
server proxy gateways) with the same interface id, e.g.

The English-speaking world has not had a lot of experience setting up
IPv6 networks so we still don't know exactly how people will use this.
One thing is sure, enterprise network designers often do not design
things the same way as ISPs do. They have different goals, different
toolsets, and different thought leaders.

--Michael Dillon

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