Subject: [Autoconf] Re: [MANET-AUTOCONF] Re: review of draft-singh-autoconf-adp-02

From: Jari Arkko <[email-masked]>
Date: Thu, 02 Feb 2006 16:01:35 +0200

Simone Ruffino wrote:

>Anyway, my personal understanding was that AUTOCONF must necessarily
>take address uniqueness into account, for two reasons: 
>Primarily, to address specific problems of MANETs: for example, if two
>nodes have the same address, routing in the *whole* MANET could possibly
>be compromised.
>  
>
Right. Yes, I think I understand this, now. Will this
happen always, or is this danger specific to some
MANET routing mechanisms?

>As a matter of fact, rfc2462 says also that DAD can be
>disabled in cases when its overhead outweighs its benefits. 
>  
>
Right. I wouldn't use compliance with RFC 2462 as the
main reason for performing duplicate detection.

>My conclusion was that a uniqueness check must be defined for MANETs,
>but that can possibly be disabled. For this reason, I would like to have
>a solution which check uniqueness using an "optimistic" approach
>(something similar to optimistic DAD). 
>  
>
Optional optimistic DAD is one approach. But that
still leaves some questions to decide. For instance, are
the manet-internal addresses and globally reachable
addresses the same or different? If they are different,
will they be allocated by the same or different mechanisms.
For instance, you could use something PACMAN-like
for the internal addresses, and then have the globally
reachable addresses allocated centrally from the gateway
(because obviously you need to be able to reach the
gateway or else these addresses aren't useful).

--Jari

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From: Christophe Jelger <[email-masked]>
Date: Thu, 02 Feb 2006 16:10:00 +0100

Hi all,

Well we have already had quite a lot of discussions related to address 
uniqueness and I strongly support Jari's point to make DAD optional 
(especially if RFC2462 allows to do so). Actually I am in favor of 
getting rid of DAD, only maintaining a minimal scheme to detect and 
resolve address collisions when they occur.

Going back to discussions with Bob Hinden (on this list in Feb. 2005 !) 
about the possible use of unique local IPv6 addresses (now RFC 4193) as 
MANET-local addresses, Bob agreed (email dated 02/24/2005) that each 
node could generate its own Global ID + subnet ID (56 bits), to be added 
to the EUI-64 (with 48 bits supposed to be unique from the MAC address). 
Moreover to make it even better, one could replace the ff:fe pattern of 
the EUI-64 with a random 16 bits pattern.

This leads to a total of 120 bits, with 80 random bits and a sequence of 
48 bits which has a very high probability of being unique. Additionaly 
the 80 bits pattern could include machine-specific data that would 
strongly increase the uniqueness of the generated address. For example, 
one could include the local date (in unix style, seconds elapsed since 
Jan. 1st 1970) when the address is generated: this is only 32 bits, but 
is a very strong anti-collision feature. Indeed 2 machines having the 
same MAC address, having generated the same random 48 bits (80-32), 
would have an address collision if they created their addresses at the 
very same (local) date !... do we really need a strong DAD mechanism to 
handle such highly improbable event ?

Now if global connectivity is required, I personaly think that using 
EUI-64 with the ff:fe pattern replaced with random bits is enough to 
guaranty address uniqueness.

Just my 2 cents ... ;-)

Regards,
Christophe

Jari Arkko wrote:
>> take address uniqueness into account, for two reasons: Primarily, to 
>> address specific problems of MANETs: for example, if two