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

Michael Richardson <> Wed, 20 November 2013 14:04 UTC

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From: Michael Richardson <>
To: "Roberta Maglione (robmgl)" <>
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Date: Wed, 20 Nov 2013 09:03:52 -0500
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Cc: "" <>, Athanasios Douitsis <>, "Bernie Volz (volz)" <>, Jouni Korhonen <>, " WG" <>, "" <>
Subject: Re: [radext] [homenet] [dhcwg] PPP, DHCPv6 and Prefix Delegation
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Roberta Maglione (robmgl) <> wrote:
    > The reason why I think a new radius would be required is because you need to
    > differentiate between the scenario where Framed-IPv6-Prefix is used to number
    > the Wan link with a separate prefix (not included in the PD - without the
    > PD_EXCLUDE) and the scenario you described where the prefix for the WAN link is
    > part of the PD and you need to copy it into the PD exclude option.

    > Today the BNG (that in this case is acting both as RADIUS Client and Delegating
    > Router) has no mean to know if the  Framed-IPv6-Prefix should be used for the
    > PD_EXCLUDE or not and in my opinion it would be better not overload the
    > sematic of the Framed-IPv6-Prefix.

If the DHCPv6 server that is constructing the PD can know what how the WAN
link is numbered, then it can include the PD_EXCLUDE based upon a simple

If one assumes the inclusion of the Framed-IPv6-Prefix in the DHCPv6 RADIUS
option added by a relay, then even if the DHCPv6 is not co-located, it could
know about the Framed-IPv6-Prefix.  That might not cover all situations
however, in particular, it won't cover cases where the WAN link was not
numbered as a result of RADIUS attributes.  Is a DHCP relay that isn't
talking to a radius server allowed to synthesize that attribute, or do we
need another way to do this?

Or we are just overthinking things?

Roberta, is PD_EXCLUDE widely implemented in CPEs that do 6204?

Michael Richardson <>, Sandelman Software Works