Re: v6 subnet size for DSL & leased line customers

["Christopher Morrow" <morrowc.lists () gmail com>]

On Jan 2, 2008 10:21 AM, Iljitsch van Beijnum <iljitsch () muada com> wrote:
> 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...

there is only one prefix so this amounts to, essentially, on/off for a
peer/transit/customer. (you can distance yourself from all of a
provider directly connected or none...)

> > > 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.

So, sure a dhcp server can do some of the work, but you may end up
with situations where customerX moves from pop1 to pop2 and if you
aggragated on pop boundaries you'll have to plan on leakages across
the boundaries, bloating your IGP some... or plan on the customer
being 'broken' until they call and get new address space. With a
'dynamic' (each login you get a randomly assigned PD from the local
pool) you'd avoid this and avoid the hassles when customerX leaves and
you all of a sudden have to deconflict customerX from
new-customer-Z... Cleanup classically has been a difficult art to
master :( (costly)

> > 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.

well see, we are almost half way there :) good think cisco bought
linksys, do linksys devices do v6? and PD and RA?

> > and v6 includes auto-renumbering for 'free' right?
>
> Yes, that must be why IPv6-capable firewalls are still hard to
> find.  :-)

define 'capable' :)