North American Network Operators Group
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Re: v6 subnet size for DSL & leased line customers

  • From: Iljitsch van Beijnum
  • Date: Wed Jan 02 10:25:54 2008

On 2 jan 2008, at 6:42, Christopher Morrow wrote:

out of curiousity how is this sort of thing supposed to be done in v6?
(traffic engineering given the '1 prefix per ISP' standard mantra)

AS path prepending, local preference, that kind of thing...

Static assignments of /56 to customers make sense to me, and that's the
assumption I've made when suggesting the addressing scheme I proposed.
Once you go static with /56s, you may as well make it easy for both
yourself and the customer to move to a /48 that encompasses the
original /56 (or configure the whole /48 for them from the outset). 

I think the assumption most folks make with DSL/cable is that
end-users get dynamic assignments from a local (to the PE device)
pool, similar to ipv4. I suppose you could do static assignments, but
there's a management payment there that might not fit within the ISP's
cost plan.

There is no "static" and "dynamic", only points along a line... Obviously you don't want your customers to renumber every day and twice on sunday, but you also don't want to keep configurations specific for each customer. A good DHCP server will keep giving you the same address until it's forced to give that address to someone else when you're not using it, or until it loses its assignment history. I assume something similar will happen here for most customers.

I presume that something accepting PD would be smart
enough to let the end-hosts/lans know when their top 56 bits
changed...

Cisco routers can change their RAs based on a new PD prefix and even align the lifetimes so the renumbering happens very smoothly.

and v6 includes auto-renumbering for 'free' right?

Yes, that must be why IPv6-capable firewalls are still hard to find. :-)