Subject: question about DHCPv6 prefix delegation

From: [email-masked]
Date: Tue, 01 Jun 2004 16:11:51 +0200

Hi All,

I have a question about DHCPv6 prefix delegation (RFC 3633).

Given the following network:

             ISP (Location of DHCPv6 server)
              |
              |
             CPE           /48
             / \
            /   \
        ---B----A---
           |    |

Is it possible to configure the DHCP server to allocate  :
- a /48 prefix to the CPE node
- and several /64 prefixes to the nodes A and B ?

Thank you for any help,

Regards,

Laurent

-- 
Laurent Clévy                
Alcatel CIT, R&I             Voice: +33 (0)1 69 63 18 34
Route de Nozay               Fax  : +33 (0)1 69 63 13 59
91460 Marcoussis             mailto:[email-masked]

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From: "Christian Strauf (JOIN)" <[email-masked]>
Date: Tue, 01 Jun 2004 21:42:11 +0200

> - and several /64 prefixes to the nodes A and B ?
I would say yes in theory, if

- the CPE acts as a DHCPv6 relay agent for A and B (see RFC3315)
- The DHCPv6 server at the ISP can deal with a relay agent

Of course, the CPE, A and B must all be DHCPv6 clients. It may be
necessary to deal with routing issues when the CPE acts as relay agent
(it must "know" how to get the relayed DHCPv6 messages to the DHCPv6
server).

I'm curious: why would you want to leave the configuration of prefixes
for A & B in the hands of the ISP rather than in the hands of the
customer (e.g. by letting the CPE act as a DHCPv6 server)?

Christian

---

From: "Tony Hain" <[email-masked]>
Date: Tue, 1 Jun 2004 14:34:00 -0700

You are asking a question which mixes technology with policy. The simple
answer to your question is YES. The complex answer is a function of the
policy at the ISP DHCP server. Will it accept requests from A & B? Are you
expecting the set of /64's allocated to A & B to be contained within the /48
at the CPE? If so what mechanism enforces that at the DHCP server? (IE: how
does the DHCP server associate A or B with the CPE?) 

What is the point of such a broken deployment model? If the expectation is
to allocate a /48 to the CPE using DHCP-PD (which it should be), then put a
DHCP server in the CPE and have it delegate /64's from that space. This
ensures that A & B get their space from the appropriate point in the
hierarchy, as well as distributes the load. Consider that it will not be
long before A & B have expanded to ~10^3 devices behind that CPE, multiple
the number of CPE by that and figure out how to scale the authentication &
association logic for a central DHCP server to ensure everything works as
expected. Then reconsider the simplicity of distributing that function to
the CPE.

Tony

> -----Original Message-----
> From: [email-masked] [mailto:[email-masked]] On Behalf Of
> [email-masked]
> Sent: Tuesday, June 01, 2004 7:12 AM
> To: [email-masked]; Ralph Droms
> Subject: question about DHCPv6 prefix delegation
> 
> Hi All,
>