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

Athanasios Douitsis <> Tue, 19 November 2013 16:07 UTC

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Date: Tue, 19 Nov 2013 18:07:46 +0200
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From: Athanasios Douitsis <>
To: "Roberta Maglione (robmgl)" <>
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Cc: "" <>, "" <>, "Bernie Volz (volz)" <>, " WG" <>, Michael Richardson <>
Subject: Re: [radext] [dhcwg] [homenet] PPP, DHCPv6 and Prefix Delegation
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On Tue, Nov 19, 2013 at 5:20 PM, Roberta Maglione (robmgl) <
> wrote:

> > Perhaps if the case is as in your example (Framed-IPv6-Prefix is
> contained by Delegated-IPv6-Prefix, but not equal) >then using the
> Framed-IPv6-Prefix for OPTION_PD_EXCLUDE makes some sense?
> Maybe it could theoretically make sense but is this a common deployment
> model? Are there any Service Providers that use or plan to use this model?


I wonder how common it is for providers to enumerate the WAN with a global
prefix. If one wants to enumerate the WAN with a global prefix one should
unavoidably have to find a /64 additionally to the /56 (or whatever is
allocated) per customer. Without PD_EXCLUDE, the framed /64 must be foreign
to the delegated /56, which means different prefix pools, double the size
of the routing table in your delegating router, etc. Basically the "3 -
Problem Background" from rfc6603 says it much better than me.

In our setup (moderate size provider with PPP links over DSL enumerated
with NDRA and then DHCPv6-PD), we use both Framed-IPv6-Prefix (global) and
Delegated-IPv6-Prefix (also global) to tell the delegating router what to
give out. Obviously these two prefixes come from different pools of global
prefixes, foreign to each other. I really don't know how common it is, but
if instead of maintaining two separate prefix pools for framed and
delegated we could just use a single pool of /56 prefixes where the framed
/64 comes from inside the corresponding /56 for each customer, that would
be indeed great.

Athanasios Douitsis