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Re: v6 subnet size for DSL & leased line customers

  • From: Mark Smith
  • Date: Tue Jan 01 08:41:49 2008

On Tue, 1 Jan 2008 12:57:17 +0100
Iljitsch van Beijnum <iljitsch@xxxxxxxxx> wrote:

> 
> On 31 dec 2007, at 1:24, Mark Smith wrote:
> 
> > Another idea would be to give each non-/48 customer the
> > first /56 out of each /48.
> 
> Right, so you combine the downsides of both approaches.
> 
> It doesn't work when ARIN does it:
> 

Well, ARIN aren't running the Internet route tables. If they were, I'd
assume they'd force AS6453 to do the right thing and aggregate their
address space. 

> *  24.122.32.0/20   4.68.1.166               0             0 3356 6453  
> 11290 i
> *  24.122.48.0/20   4.68.1.166               0             0 3356 6453  
> 11290 i
> *  24.122.64.0/20   4.68.1.166               0             0 3356 6453  
> 11290 i
> *  24.122.80.0/20   4.68.1.166               0             0 3356 6453  
> 11290 i
> *  24.122.96.0/20   4.68.1.166               0             0 3356 6453  
> 11290 i
> *  24.122.112.0/20  4.68.1.166               0             0 3356 6453  
> 11290 i
> *  24.122.128.0/20  4.68.1.166               0             0 3356 6453  
> 11290 i
> *  24.122.144.0/20  4.68.1.166               0             0 3356 6453  
> 11290 i
> *  24.122.160.0/20  4.68.1.166               0             0 3356 6453  
> 11290 i
> *  24.122.176.0/20  4.68.1.166               0             0 3356 6453  
> 11290 i
> *  24.122.192.0/19  4.68.1.166               0             0 3356 6453  
> 11290 i
> *  24.122.224.0/20  4.68.1.166               0             0 3356 6453  
> 11290 i
> *  24.122.240.0/20  4.68.1.166               0             0 3356 6453  
> 11290 i
> 
> And it's unlikely to work here: for those standard size blocks, you  
> really don't want any per-user config: you want those to be assigned  
> automatically. But for the /48s you do need per-user config, if only  
> that this user gets a /48. So these two block sizes can't  
> realistically come from the same (sub-) range.

Maybe I'm not understanding this correctly. Are you saying that
customers who have a /56 would get dynamic ones i.e. a different one
each time they reconnect? If they've got a routed downstream topology,
with multiple routers and subnets (because of course, they've got 256
of them), I don't think customers will be very happy about having to
renumber top /56 bits if e.g. they have a DSL line sync drop out and
get a different /56.

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).

Regards,
Mark.

-- 

        "Sheep are slow and tasty, and therefore must remain constantly
         alert."
                                   - Bruce Schneier, "Beyond Fear"