Subject: [nemo] New draft on prefix delegation

From: "T.J.Kniveton" <[email-masked]>
Date: Tue, 19 Oct 2004 02:24:42 -0700

Hello,

Pascal and I have put together a draft that talks about how prefix  
provisioning and delegation can happen at the NEMO protocol level. This  
is intended to be a complementary process to what Ralph has described,  
that happens at the back end and DHCPv6 servers. Ideally, if the WG  
thinks this approach is good, we would like to better integrate the  
DHCPv6 back end approach (and possibly others, if proposed).

http://www.mobilenetworks.org/nemo/drafts/draft-kniveton-nemo-prefix- 
del-00.html (html)
or
http://www.mobilenetworks.org/nemo/drafts/draft-kniveton-nemo-prefix- 
del-00.txt (text)

This draft is a work in progress, since we have changed the formats  
quite a bit while writing -00, the sections might not all match up so  
please feel free to point out discrepancies.

While the draft didn't make it to the IETF repository by yesterday's  
-00 cutoff, we would still encourage anyone interested to read it  
before the Washington meeting.

-TJ & Pascal

---

From: Alexandru Petrescu <[email-masked]>
Date: Tue, 19 Oct 2004 15:00:54 +0200

Hi TJ, Pascal, thank you for putting up this draft proposing to request
assignment of prefixes with a BU and assignment confirmation with BAck.
  This is an interesting idea.

Other methods could be DHCP, and even piggybacking with Mobile Prefix
Discovery or with Dynamic Home Agent Address Discovery, etc.  I'm
tempted to favor DHCP, see below.

T.J.Kniveton wrote:
> provisioning and delegation can happen at the NEMO protocol level. 
> This is intended to be a complementary process to what Ralph has 
> described, that happens at the back end and DHCPv6 servers. Ideally,
>  if the WG thinks this approach is good, we would like to better 
> integrate the DHCPv6 back end approach (and possibly others, if 
> proposed).

Would a NEMO-PD-enabled HA use a DHCPv6 server to manage the prefix
allocation? I suppose this is what you mean by "integrate the DHCPv6
back end approach".

I personally would go for an entirely DHCP-based solution. Allocating
and freeing prefixes (and addresses) is usually large programs, risky to
run in the kernel space. HA is usually in kernel, DHCP server in app
space. Exceptions there are to this, ok, but still.

DHCP has other advantages as well. It already has hierarchical concepts
(Server and Relay), while HA has not. This could be used with a large
moving network served by only a MR and that has many internal FR's
(fixed). Using DHCP, MR may act as a Client and request a short prefix
from its home DHCP Server and simultaneously act as a Relay (or Server)
and assign a longer prefix to its FR's acting respectively as Clients.

On the contrary, delegating prefixes in the BU/BAck makes it impossible
for FR's to acquire a prefix, since they don't run Mobile IPv6.

An additional advantage of DHCP is reusing the complex management
software that a DHCP does for addresses (allocate, free, re-allocate,
manage fragmentation), etc.  HA has no such functionality that could be
reused.

> CorId: A Correlator that is set by the MR in order to associate a MNP
>  request with the prefix given in the confirmation.  There can be at 
> most one active prefix associated with each Correlator.  This 
> mechanism ensures the uniqueness of the allocation of a prefix, 
> should either the BU or the BA be lost in transit.

In order to guarantee uniqueness of the assignment, the association
should base also on the Home Address because different MR's may generate
same CorID.  With DHCP, this "uniqueness" is based on the MAC address
and with a Transaction ID.

With DHCP there are options for releasing addresses.  On the contrary
BU-BAck PD does not have a feature to release a prefix.  Releasing is
important, because if an MR goes asleep another MR can re-use that prefix.

With DHCP there are options for going in "dormant" mode and back up
again, minimizing the amount of messages exchanged.

With DHCP there are possibilities to update the DNS as well (although no
prefixes in the DNS, but gateway addresses may be needed).

When DHCP assigns/removes an address, it automatically adds/removes
routes corresponding to that address.  This is re-usable software,
essential when assigning a prefix.  The draft in question proposes
similar features (transient/persistent).

DHCP has a message CONFIRM, sent by the Client.  BU/BAck has a MNP
Confirmation option, but sent by the HA :-)

Finally, my oppinion is that the method used by the MIP6 WG to assign a
Home Address to MN should be used by NEMO too, for prefixes.  That is,
if MIP6 MN generates the Home Address from DHAAD+MPD then NEMO should do
MNP from MPD.  If MIP6 assigns the Home Address from DHCP, then NEMO
should do MNP from DHCP too.  Same with BU/BAck.

> Proposing a new, specific solution might seem irrelevant when a 
> standard, generic mechanism already exists: in this case, the DHCPv6 
> Prefix Delegation.  In fact, it is  possible for the Home Agent to 
> act as a  DHCPv6PD Delegating Router.  This solution presents the 
> advantage of reusing existing standard flows from RFC3633 [6].

I agree with this.

> Yet, in a deployment where the MNPs are preassigned to the MR, a AAA 
> server, interfacing with the HA, and eventually coupled with a 
> provisioning system in its back-end, can provide the required service
>  for assigning and authorizing the prefixes to the MRs; in such a 
> case, the value of implementing a DHCPv6PD server is highly arguable.
> 
> 
Yes, it is highly arguable.  I do not know whether a Radius server uses
DHCP or not.  I do not know whether a Radius server can talk to a IPv6
HA either...

What do you think...

Alex

---

From: Vijay Devarapalli <[email-masked]>
Date: Tue, 19 Oct 2004 19:04:51 -0700

> should do MNP from DHCP too.  Same with BU/BAck.

there was such a draft proposed in March 2003 extending the Mobile
Prefix discovery mechanism to delegate prefixes for the Mobile Router.
see 
http://www.mobilenetworks.org/nemo/drafts/draft-paakkonen-nemo-prefix-delegation-00.txt

at that time, the NEMO WG rejected the draft saying that we already
have a mechanism through DHCPv6.

Vijay

---

From: Alexandru Petrescu <[email-masked]>
Date: Wed, 20 Oct 2004 12:18:53 +0200

Vijay Devarapalli wrote:
>> Finally, my oppinion is that the method used by the MIP6 WG to 
>> assign a Home Address to MN should be used by NEMO too, for 
>> prefixes.  That is, if MIP6 MN generates the Home Address from 
>> DHAAD+MPD then NEMO should do MNP from MPD.  If MIP6 assigns the 
>> Home Address from DHCP, then NEMO should do MNP from DHCP too. Same
>> with BU/BAck.
> 
> Prefix discovery mechanism to delegate prefixes for the Mobile 
> Router. see 

IMHO the best way to assign addresses and prefixes is via DHCP.  It also
makes sense to use the same mechanism in MIP6 and NEMO, and even better
- MIP4, MIP6 and NEMO.

I've also noticed a new idea of assigning the Home Address with IKE...
would this work for MNP's?

Alex