Subject: Prefix Delegation using ICMPv6

From: "Syam Madanapalli" <[email-masked]>
Date: Wed, 23 Aug 2006 07:25:54 +0530

A new draft has been published for prefix delegation using ICMPv6.
http://www.ietf.org/internet-drafts/draft-rao-ipv6-prefix-delegation-00.txt

Please review and provide comments/suggestions.

Thanks,
Syam

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From: Ole Troan <[email-masked]>
Date: Wed, 23 Aug 2006 14:57:16 +0900

I don't understand the rationale for this work either.

the first PD proposal (by Brian Haberman) was indeed based on using
ICMP as transport. separate message types instead of
piggy-backing on RS/RA though. as we continued to develop that
mechanism we realised that we were pretty much reinventing the DHCP
protocol machine. that realisation led to specifying it as an DHCP
option instead of as a new protocol.

a technical comment on your proposal; how do you plan to support
shared links with multiple requesting routers? RAs are typically
multicast.

/ot

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From: "Syam Madanapalli" <[email-masked]>
Date: Wed, 23 Aug 2006 13:24:41 +0530

Hi,

> option instead of as a new protocol.

Currently DHCP mechanism works only between routers whereas this
new mechanism works for end hosts. This draft just introduces a flag
in Prefix Information Flag (PIO) to indicate that the prefix is unique for
the device. And another flag in RS to inform the routers that the host is
looking for a unique prefix.

Currently we use RS/RA to discover the prefixes available on the link
(shared prefixes), I think it is natural to extend this for hosts to get unique
prefixes.

Also, the subnet model that NetLMM WG wants to choose is to have
a unique prefix for each MN. These extensions for RS/RA allows
NetLMM hosts to be able to get unique prefixes in a better compared
to current RS/RA messages.

> shared links with multiple requesting routers? RAs are typically

Typically RAs are sent in unicast in response to an RS. When the router
receives an RS with the prefix delegation request flag, the router must
send an unicast RA.

-Syam

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From: Eliot Lear <[email-masked]>
Date: Wed, 23 Aug 2006 10:44:22 +0200

Syam Madanapalli wrote:
> new mechanism works for end hosts. 

The difference between a router and a host is a routing process and a
willingness to forward packets, not how it interprets ICMP or whether it
can parse DHCP.

Eliot

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From: Mohacsi Janos <[email-masked]>
Date: Wed, 23 Aug 2006 10:52:18 +0200 (CEST)

> receives an RS with the prefix delegation request flag, the router must

I did not see any implementation until now, that sending RAs in unicast in 
response to an RS. The specification allows unicast RAs, but it less 
common....

Regards,

Janos Mohacsi
Network Engineer, Research Associate, Head of Network Planning
NIIF/HUNGARNET, HUNGARY
Key 00F9AF98: 8645 1312 D249 471B DBAE  21A2 9F52 0D1F 00F9 AF98

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From: Brian E Carpenter <[email-masked]>
Date: Wed, 23 Aug 2006 13:20:51 +0200

> a unique prefix for each MN. 

What is a "prefix"? In IPv6 it can be anywhere between /1 and
/127. (If it's longer than /64 it means you aren't using
ND, but ND is additional to the basic IPv6 architecture).

NetLMM is indeed using an unconventional model, as I discovered
when reviewing draft-ietf-netlmm-nohost-ps with my IESG hat on.
Are you asserting that DHCP won't be used in NetLMM deployments?

     Brian

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From: Ralph Droms <[email-masked]>
Date: Wed, 23 Aug 2006 07:34:40 -0400

Questions in line...

- Ralph

> looking for a unique prefix.

Perhaps we need to back up and understand the application better.  In  
DHCPv6 PD, we labeled the client node as "requesting router" because  
PD seems only applicable in the case where the DHCPv6 client is  
acting as a router between some links (to which the delegated  
prefixes will be assigned) and the interface through which the  
delegated prefix was assigned.  Is the ICMP PD proposal addressing  
some different scenario?  If so, where can I learn about it?

> (shared prefixes), I think it is natural to extend this for hosts  

Where are these unique prefixes being used?  On the link between the  
aggregation device and the CPE or between the CPE and the subscriber  
CPEs in the diagram below?

                  ______________________                 \
                 /                      \                 \
                |    ISP core network    |                 \
                 \__________ ___________/                   |
                            |                               |
                    +-------+-------+                       |
                    |  Aggregation  |                       | ISP
                    |    device     |                       | network
                    |  (delegating  |                       |
                    |    router)    |                       |
                    +-------+-------+                       |
                            |                              /
                            |DSL to subscriber            /
                            |premises                    /
                            |
                     +------+------+                     \
                     |     CPE     |                      \
                     | (requesting |                       \
                     |   router)   |                        |
                     +----+---+----+                        |
                          |   |                             | Subscriber
   ---+-------------+-----+- -+-----+-------------+---      | network
      |             |               |             |         |
+----+-----+ +-----+----+     +----+-----+ +-----+----+    |
|Subscriber| |Subscriber|     |Subscriber| |Subscriber|   /
|    PC    | |    PC    |     |    PC    | |    PC    |  /
+----------+ +----------+     +----------+ +----------+ /

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From: Jari Arkko <[email-masked]>
Date: Wed, 23 Aug 2006 15:25:26 +0300

>> a unique prefix for each MN. 
Having a unique prefix for each MN is not the same as a
requirement to perform prefix delegation. Netlmm hosts
are required to work with existing stacks, and I would
generally expect them to use SLAAC or DHCP in the
normal manner. Just that the network advertises a
different prefix for each mobile node, e.g., on the
point to point link that the node is on. Details to
be worked out, this is still work in progress.

I would also expect that Netlmm to not disturb
other functions. So if someone wanted to deploy
a Netlmm network with an additional prefix
delegation via DHCP for mobile routers -- that
should be possible.

In short, I don't think Netlmm can be used as an
argument for a new prefix delegation scheme.

--Jari

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From: "Syam Madanapalli" <[email-masked]>
Date: Wed, 23 Aug 2006 22:44:09 +0530

Hello Ralph,

> some different scenario?  If so, where can I learn about it?

What I mean is that the prefix delegation mechanism can be used
to assign unique prefixes for the hosts. Prefix Delegation and assigning
unique prefixes may be different conceptually but the same mechanism
can be used for both.

> CPEs in the diagram below?

It's between CPE and Subscriber PC - unique prefixes for subscriber PCs.

- Syam

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From: "James Kempf" <[email-masked]>
Date: Wed, 23 Aug 2006 10:31:06 -0700

Yes, I think there needs to be a distinction made between:

 a) prefix delegation, in which the upstream router gives the prefix to the 
downstream node in the expectation that the downstream node will be routing 
to nodes downstream from it,
b) prefix assignment, in which the upstream router advertises a prefix in an 
RA for the link, assigning the prefix to that link for nodes to use in 
address autoconfiguration and for other purposes.

Assigning a unique prefix per mobile node works with either of these, in the 
first case, the downstream node is a router, in the second, it may or may 
not be a router but it won't route the prefix further since the upstream 
router has assigned the prefix to the link between the two.

In sum, as Jari says below, I don't see a need for a new prefix delegation 
or assignment mechanism for NETLMM.

        jak

----- Original Message ----- 
From: "Jari Arkko" <[email-masked]>
To: "Syam Madanapalli" <[email-masked]>
Cc: "Brian E Carpenter" <[email-masked]>; "IETF IPv6 Mailing List" 
<[email-masked]>
Sent: Wednesday, August 23, 2006 5:25 AM
Subject: Re: Prefix Delegation using ICMPv6

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From: Ralph Droms <[email-masked]>
Date: Wed, 23 Aug 2006 13:32:59 -0400

Syam - I'm feeling really dense at this point.  I don't understand  
"unique prefix for host" and assigning the unique prefix for each  
host between the CPE and the subscriber PC.  In your scenario, what  
devices participate in PD in the diagram I included?  Is there a  
description of the scenario I can read?

- Ralph

On Aug 23, 2006, at 1:14 PM, Syam Madanapalli wrote:

>>                          |   |                             |  
>> Subscriber

---

From: "Syam Madanapalli" <[email-masked]>
Date: Wed, 23 Aug 2006 22:34:01 +0530

On 8/23/06, Jari Arkko <[email-masked]> wrote:
> requirement to perform prefix delegation.

I am not sure if there is any difference as for as protocol
is concerned. The mechanism specified in the draft can be
used to assign unique prefixes for the hosts as well as for
prefix delegation.

> Netlmm hosts

Sure, I was just saying that, this mechanism can be
useful in the NetLMM scenario as the MAG requires
some changes to advertise unique prefixes for each MN
for SLAAC. Instead of changing the default router behavior,
it is easy extend the RS/RA for assigning unique prefixes.

If they want to use DHCP, sure it works.

- Syam

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From: "Syam Madanapalli" <[email-masked]>
Date: Fri, 25 Aug 2006 07:55:37 +0530

Hello Ralph,

CPE (RR) in your diagram participate in prefix delegation.
And CPE and Subscriber PCs can use the same prefix delegation
mechanism to assign unique prefixes to the subscriber PCs.
This can be useful in scenarios where unique prefix assignment
is required on a shared link.

-Syam