IPv6 Addressing Help

Jeroen Massar jeroen at unfix.org
Fri Aug 14 10:17:30 CDT 2009

Chris Gotstein wrote:
> We are a small ISP that is in the process of setting up IPv6 on our
> network.  We already have the ARIN allocation and i have a couple
> routers and servers running dual stack.  Wondering if someone out there
> would be willing to give me a few pointers on setting up my addressing
> scheme?

Strange, I recall that you had to submit one when requesting address
space from ARIN. Why don't you use that one?

> I've been mulling over how to do it, and i think i'm making it
> more complicated than it needs to be.  You can hit me offlist if you
> wish to help.  Thanks.

It all depends on your network and how you want to set it up, but for
the sake of internal aggregation:
 * Determine the expected amount of IPv6 customers at a certain
   location for the next X years, making X > 2 (though 10 is probably a
   better idea, just in case, if don't want to do it again ;) )
 * Take that number round it up to a power of 2
 * Every customer gets a /48, you know the number, which is a power of
   2, thus root it, and you know how many bits you need at that site

   eg expect 200 customers, round to power of 2 thus 256, which is 2^8,
   thus you will need a /48 + 8 bits = /40 at that location.

You now know how much address space you need at that location for the
next X years.

Repeat that for all your locations / routing areas, basically the PoPs
or termination points of your customers; or if you are really big do
that per city/town/suburb. Keep enough space (the rounding helps there
quite a bit, especially with numbers like 50k customers ;)

Now you have an overview of what you expect to be allocating at each and
every site. To add a little growth/future proof and to make live easy,
you could either opt at this stage to round everything off to 'nice'
numbers, eg only use /40's or /36's per PoP. Thus making everything the
same, or doing things like grouping smaller PoPs together.

Then when you have done that, take those blocks, and try to squeeze them
a bit together. You should now have arrived to the address plan that you
originally submitted to ARIN.

Fill those blocks into a nice database, roll a PHP/shell/perl/whatever
script to spit out your router configuration and presto: you are done.

Enjoy the weekend ;)


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