Subject: IPv6 PD

From: [email-masked]
Date: Mon, 24 Jul 2006 21:06:49 -0500 (CDT)

Hi Fred/all,

The former subject line became far too unwieldy, and the subject of IPv6 referred to in the attached exchange is of interest.

IPv6 PD is between two routers, not a router and an end host. Using ISP parlance, the delegating router is the ISP PE (delegating) router and the requesting router is the CE router. 

The abstract of RFC 3769 which defines the IPv6 PD requirements says: "This document describes requirements for how IPv6 address prefixes
should be delegated to an IPv6 subscriber's network (or "site")." Section 1 echoes this point. It's logical to infer from Section 4 that the CPE is the requesting router (not host): "A rogue PE can issue bogus prefixes to a requesting router."

Given the way RFC 3633 is written, there is reason to pre-suppose that the client will behave as a router. In DHCPv6 PD, the ISP router that serves as the DHCPv6 server is the delegating router. The CPE that serves as the DHCPv6 client is the requesting router (Section 3). Section 5.1 illustrates an example architecture wherein this is shown. The point is also made that the requesting router subnets whatever prefixes are delegated to it and assigns those longer prefixes to links within the subscriber network.

a. There has neither ever been nor is there now a standard defining ICMPv6 PD. There are however at least three expired drafts (of which I am aware) on the subject:
i) draft-haberman-ipngwg-auto-prefix-02.txt
ii) draft-bykim-ipv6-hpd-01.txt
iii) draft-arunt-prefix-delegation-using-icmpv6-00.txt
b. There might need to be a separate ICMPv6 packet type defined by the IANA for ICMPv6 PD. Note that all three of the aforementioned drafts define at least one such type. None of these exist: icmpv6-parameters.

>From: "Templin, Fred L" <[email-masked]>
>Date: 2006/07/24 Mon PM 07:11:38 CDT
>To: Iljitsch van Beijnum <[email-masked]>
>Cc: IETF IPv6 Mailing List <[email-masked]>
>Subject: RE: Forward: Re: Last Call: 'IPv6 Router Advertisement OptionforDNS	Configuration' to	ExperimentalRFC(draft-jeong-dnsop-ipv6-dns-discovery)

>> Prefix delegation is a feature used by routers, not by hosts.
>
>I don't understand this point as it relates to the question of
>whether/not DHCPv6 will be needed, and the more I think about
>it the more irrelevant it seems. Prefix delegation is a feature
>used by clients of a prefix delegation server - in DHCPv6, they
>are the DHCP client and DHCP server. What the client actually
>*does* with any delegated prefixes is up to the client and
>there is no reason to pre-suppose that it will necessarily
>behave as a router.
>
>Again, the question is whether there is (or will be) a
>way of doing prefix delegation w/o DHCPv6? (If so, would
>it be any better than DHCPv6 - or just different?)
>
>Fred
>[email-masked]
>
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---

From: "Templin, Fred L" <[email-masked]>
Date: Tue, 25 Jul 2006 08:41:51 -0700

Hi Tim, 

> IPv6 PD is between two routers, not a router and an end host.
> Using ISP parlance, the delegating router is the ISP PE
> (delegating) router and the requesting router is the CE router.

The point of router vs end host is really aside from the original
question of whether DHCPv6 would be useful for anything, and prefix
delegation was cited as an example where DHCPv6 might be useful.

That said, even though the RFC3633 text is couched in terms of
"delegating router" and "requesting router", I don't see anything
wrong with the "requesting router" being an end host that may/may
not become a router at some point in the future. A "requesting
router" could, for example, request a /64 and then assign one or
a few addresses from the /64 to its interfaces w/o ever actually
becoming a router. I also don't see anything wrong with an end
host using DHCP prefix delegation to request a /128, but I
wouldn't be surprised if this has already been discussed
and/or debated elsewhere.

Fred

---

From: Iljitsch van Beijnum <[email-masked]>
Date: Thu, 27 Jul 2006 13:11:24 +0200

> not become a router at some point in the future.

Yeah right. Maybe my iPod will become a router in the future. Better  
get a prefix for it now.

> A "requesting
> host using DHCP prefix delegation to request a /128

There is a different mechanism for giving out individual addresses  
using DHCPv6 so this doesn't make much sense. This is just way too  
heavy a mechanism to use for individual hosts: you need to install  
routes for all delegated prefixes and possibly redistribute those in  
a routing protocol. Also, this only works when the server and client  
are on the same link, while normal DHCP can be done over several hops  
by having a router relay the DHCP messages.

---

From: "Templin, Fred L" <[email-masked]>
Date: Thu, 27 Jul 2006 09:46:40 -0700

> Yeah right. Maybe my iPod will become a router in the future. Better  

I don't see anything wrong with a low-end device being a router. 

> Also, this only works when the server and client  
> are on the same link,

I don't see anything wrong with the "link" being a tunnel.

Fred

---

From: Ralph Droms <[email-masked]>
Date: Thu, 27 Jul 2006 13:43:29 -0400

The dhc WG is extending DHCPv6 PD to work across relay agents:
draft-ietf-dhc-dhcpv6-agentopt-delegate-00.txt

- Ralph

---

From: Iljitsch van Beijnum <[email-masked]>
Date: Thu, 27 Jul 2006 20:33:14 +0200

> I don't see anything wrong with a low-end device being a router.

Me neither, but that doesn't mean all low-end devices need IPv6  
address space just in case.

> I don't see anything wrong with the "link" being a tunnel.

Well, why do you need DHCPv6 then? Just use the same provisioning  
system for giving out address space that was used to configure the  
tunnel.

---

From: "Templin, Fred L" <[email-masked]>
Date: Thu, 27 Jul 2006 11:37:48 -0700

> system for giving out address space that was used to configure the  

DHCPv6 already provides an excellent provisioning system for this; see:

http://www.ietf.org/internet-drafts/draft-templin-autoconf-netlmm-dhcp-0
2.txt

Fred

---

From: Alexandru Petrescu <[email-masked]>
Date: Fri, 28 Jul 2006 17:34:22 +0200

> iii) draft-arunt-prefix-delegation-using-icmpv6-00.txt

Doing it with Mobile IPv6:
draft-ietf-nemo-prefix-delegation-00 August 2005.

Alex