Subject: RE: DAD vs. DIID

From: "Richard Draves" <[email-masked]>
Date: Thu, 22 Aug 2002 11:21:48 -0700

> > > Yes, my stack allows defining any address manually. I don't
> > > code programs that pretend to be more clever than the user. I 
> > > assume if the user wants some specific address, then he/she 
> > > will get it (if it passes DAD). In manual configuration I 
> > > assume user KNOWS from that the address will not collide with 
> > > autoconfigured (as a root you can always shoot your foot).
> > 
> > This doesn't make sense. Manually-configured addresses the 
> ones that 
> > most need DAD, because humans are the part of the system 
> that is most 
> > likely to screw up and inadvertently configure a duplicate.
> 
> Umm.. I specifically said: "if it passes DAD". What other 
> tests I'm supposed to do when a user manually configures full 
> address for the node?

You say "I assume the user KNOWS" and "as a root you can always shoot
your foot". I don't understand the details of your implementation, but
from your description it sounds like you are assuming a knowledgeable
user and if the user is wrong then the user is screwed. My point is that
assuming users behave correctly is bad design.

Rich

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From: Markku Savela <[email-masked]>
Date: Thu, 22 Aug 2002 21:42:50 +0300

> From: "Richard Draves" <[email-masked]>

> assuming users behave correctly is bad design.

A bit off topic, but as a Linux user who occasionally is forced to use
Microsoft products... Yes, I have painfully experienced the
philosophy: "user doesn't know anything, program knows better", and
have hard time turning a lot of automation off the applications,
before they become usable. :-)

However, back to topic...

...at least in my view, the normal IPv6 way is the
"autoconfiguration", especially for clueless users. I consider manual
configuration of address to be rather extreme rare case, which normal
users don't need to worry about. If this is not true, one of rather
important IPv6 design goals has failed!

My point is that autoconfiguration with DAD optimization has been in
RFC for long time. Anyone designing alternate address configuration
mechanisms should take (and should have taken) this fact into design.

To get forward on this, can we go through other existing address
configuration mechanisms, and see how they can avoid colliding with
*autoconfigured* addresses.

- user manually configures address (avoidance: just hope you are lucky
  :-)

- DHCP (avoidance suggestions:
  (a) don't advertise prefix with A=1 on the link, all addressess are
      from DHCP or manual.
  (b) have two prefixes on the link, advertise only one with A=1, and
      give DCHP addresses from the other
  (c) allocate DHCP address with ID range such that is not used by the
      default autoconfigure (should not be difficult to find).

I don't know others at the moment.

In my view, the "collision avoidance" policy can be locally agreed on
the site (or for a link). Taylor it to the local needs.