v6 subnet size for DSL & leased line customers

Wed Jan 2 15:21:32 UTC 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.  :-)