Subject: [Autoconf] updated MANET addressing model draft

From: Emmanuel Baccelli <[email-masked]>
Date: Thu, 24 Sep 2009 13:38:59 +0200

Hi all,
an updated version of the MANET addressing model draft has just been
published. It integrates comments received during and after the last IETF
meeting, including some advisory text about IPv6 Link Local addresses,
heavily inspired from Erik Nordmark's initial proposal on this topic.

http://www.ietf.org/id/draft-baccelli-autoconf-adhoc-addr-model-02.txt

Please review it thouroughly, and give us some feedback.

Regards,

Emmanuel

---

From: Emmanuel Baccelli <[email-masked]>
Date: Tue, 29 Sep 2009 17:42:32 +0200

Hi all,

Please do let us know your feedback on the updated doc
http://www.ietf.org/id/draft-baccelli-autoconf-adhoc-addr-model-02.txt

Silence may be interpreted as violent agreement with its content ;)

Let's move on quickly with this, while we still have time before Hiroshima!

Cheers,

Emmanuel

---

From: "Teco Boot" <[email-masked]>
Date: Wed, 30 Sep 2009 14:19:28 +0200

Hi Emmanuel,

Here some (not retired :-) comments.

> 4.  IP Subnet Prefix Configuration
>
>   If the link to which an interface connects enables no assumptions of
>   connectivity to other interfaces, the only addresses which can be
>   assumed "on link", are the address(es) of that interface itself.
>   Note that while IPv6 link-local addresses are assumed to be "on
>   link", the utility of IPv6 link-local addresses is limited as
>   specified in Section 6.2.
 
I posted earlier that adding the link-local topic is not needed.
I suggested the text could be changed in:

   If the link to which an interface connects enables no assumptions of
   connectivity to other interfaces, the only addresses which can be
   assumed reachable, are the address(es) of that interface itself.

This circumvents the "on-link" discussion, which we can continue forever.
We better don't.

On 6.2 IPv6 Model:

I am fine with:
>   Note that while an IPv6 link-local address is assigned to each
>   interface as per [RFC4291], in general link-local addresses are of
>   limited utility on links with undetermined connectivity, as neighbors
>   may be constantly moving in and out of reachability.  The known
>   limitations are:
 <skip>
>   Therefore MANET autoconfiguration solutions will primarily focus on
>   configuring IP addresses that are not IPv6 link-local.

But I think the left out "known limitations" shall be verified for 
correctness and not being "opinions".

>   o  Even if tested for local uniqueness at one moment using Duplicate
>      Address Detection [RFC4862], a duplicate link-local address might
>      appear as a neighbor the next moment and DAD would not detect
>      that.

This is very true for all unicast address types. Link-local is no exception
at all!!!

To rephrase Charlie P. his comment on my recent posting: 
>I think we ought, generally speaking, to try to avoid (ii) at this point
>in the discussion.
(ii is DAD)

>   o  There is no mechanism to ensure that IPv6 link-local addresses are
>      unique across multiple links, hence they can not be used to
>      reliably identify routers.

I remember the RouterID topic was discussed shortly some time ago (IETF ??).
The opinion was that we shall stay away from this topic.

Also, I do not agree. Link-locals can perfectly be used as RouterID, 
as long as the Interface-ID is unique. And this can be ensured in 
many cases, if not all. One approach of Autoconf could be making sure
Interface-IDs are unique. Then, these can be used for whatever unicast 
Address type. We have to deal with globals one day. The sooner the better.

>   o  Routers cannot forward any packets with link-local source or
>      destination addresses to other links (as per [RFC4291]) while most
>      of the time, routers need to be able to forward packets to/from
>      different links.

This is very true. True in every IPv6 network. I don't see a reason to
repeat 
this here. Or I miss something.

Maybe the intended limitation was providing reachability on links with 
"RFC4861 asymmetric reachability". When IPv6 routers do not forward packets
with link-local source or destination, nodes on such a link may have or 
may not have connectivity using link-locals. The MANET protocol would not 
"repair" this. With MANET-local or globals, there is no such limitation in
connectivity.
On the other hand, some protocols or applications require that packets
are not forwarded, even on the same link. Then, link-locals can be utilized.
MANET routing protocols are a perfect example for this.

Suggested text:

  Routers cannot forward any packets with link-local source or
  destination addresses to other links (as per [RFC4291]). In general,
  routers do not forward such packets. This would limit connectivity
  between MANET nodes. For this reason, link-local addresses shall be 
  used only for protocols that require one-hop limited delivery of packets.

The complete text added in 6.2 would be:

   Note that while an IPv6 link-local address is assigned to each
   interface as per [RFC4291], in general link-local addresses are of
   limited utility on links with undetermined connectivity, as neighbors
   may be constantly moving in and out of reachability.  

   Routers cannot forward any packets with link-local source or
   destination addresses to other links (as per [RFC4291]). In general,
   routers do not forward such packets. This would limit connectivity
   between MANET nodes. For this reason, link-local addresses shall be 
   used only for protocols that require one-hop limited delivery of packets.

   MANET autoconfiguration solutions will primarily focus on 
   configuring IP addresses that are not IPv6 link-local.

I hope everybody can agree on this text.

Regards,
Teco

Van: [email-masked] [mailto:[email-masked]] Namens
Emmanuel Baccelli
Verzonden: dinsdag 29 september 2009 17:43
Aan: [email-masked]
Onderwerp: Re: [Autoconf] updated MANET addressing model draft

Hi all,

Cheers,

Emmanuel

On Thu, Sep 24, 2009 at 1:38 PM, Emmanuel Baccelli
<[email-masked]> wrote:
Hi all,

Regards,

Emmanuel

---

From: "Teco Boot" <[email-masked]>
Date: Wed, 30 Sep 2009 14:54:49 +0200

Hi Emmanuel,

Another oldie:

Appendix A.  Open Issues
> Global Uniqueness Requirements -  it remains to be determined whether
>      or not the scope of AUTOCONF includes applications other than
>      routing protocols running on the router, which may communicate
>      with outside the routing domain and which for that, require
>      globally unique addresses.
>

Out of our charter:
>Ad hoc nodes may also need to
>configure globally routable addresses, in order to communicate with
>devices on the Internet.

For me it is clear that configuring globally routable addresses is in scope.
I think I just repeat others here.

Regards, Teco.

Hi all,

Cheers,

Emmanuel

Regards,

Emmanuel