Re: [dhcwg] [radext] [homenet] PPP, DHCPv6 and Prefix Delegation

[Athanasios Douitsis <[e-mail]>]

On Wed, Nov 20, 2013 at 4:08 PM, Michael Richardson
<[e-mail]>wrote:

> Athanasios Douitsis <[e-mail]> wrote:
>     > Indeed in a scenario where all the requesting routers connecting to a
>     > delegating router (BNG) would have PD_EXCLUDE capability, using the
>     > Framed-IPv6-Prefix to infer what to put into the OPTION_PD_EXCLUDE
> field is
>     > sufficient.
>
>     > But if there is a mix of PD_EXCLUDE-capable and not capable
> requesting clients,
>     > the situation becomes more complex. The fundamental problem is that
> Prefix
>     > Delegation usually happens after the RADIUS exchange, so the RADIUS
> server
>     > cannot really know whether the customer is exclude-capable or not.
>
> Note that CPEs ought to be smart enough to exclude the subnet that their
> WAN
> link is in, but it's certainly the case that many are not yet that smart.
> (the dnsmasq PD implementation was missing related smarts at first)
>
>     > If, for example, the client is not exclude-capable, then having the
> RADIUS
>     > return a Framed-IPv6-Prefix that is part of the  (greater)
>     > Delegated-IPv6-Prefix is problematic for obvious reasons. In fact,
> I, for one,
>     > cannot wrap my head around a way to cover both cases
> (exclude-capable and
>     > non-exclude-capable) using only the two existing RADIUS attributes
> *and* at the
>     > same time maintain backwards compatibility with old customers.
>
> If the CPE is not EXCLUDE capable, and not smart enough to avoid the WAN
> link, then it doesn't matter what the set of attributes returned is, does
> it?
> Assuming simple minded prefix assignment by CPEs, if they start at subnet
> "1", then using subnet "0" probably works.  But, using subnet "ff" for the
> WAN link is perhaps simpler.



Hello Michael,

When I said "problematic" yesterday, I meant problematic for the delegating
router. If the other side (requesting router - CPE) is not exclude-capable
then is it not illegal for the delegating router to delegate a prefix and
at the same time use part of it to enumerate one its interfaces? So a set
of attributes where the Framed-IPv6-Prefix is contained in the
Delegated-IPv6-Prefix may result in error.

Apologies if I didn't understand correctly what you are saying.

Kind regards,
-- 
Athanasios Douitsis