Subject: Re: Question about precluding use of autonomous address-configuration

From: JINMEI Tatuya / 神明達哉<[email-masked]>
Date: Wed, 02 Nov 2005 14:19:15 +0900

>>>>> On Mon, 31 Oct 2005 14:17:17 -0500, 
>>>>> Ralph Droms <[email-masked]> said:

> Suppose the nodes on a link are to be restricted to the use of addresses
> assigned through DHCP, and precluded from the use of autonomous address-
> configuration.

> It seems there are two ways to accomplish this goal:

> 1) Don't include any prefixes in router advertisements

> 2) Include the prefixes assigned to the link in router advertisements,
>    with the A (autonomous address-configuration) flag set to FALSE

> There may be a subtle problem with (2): the text in RFC 2462 does not
> include RFC 2119 words absolutely precluding the use of autonomous
> address-configuration:

>     a) If the Autonomous flag is not set, silently ignore the
>        Prefix Information
>        option.

> Note the lack of "MUST" before "silently ignore".

I cannot speak for the authors/designers, but my interpretation is
that there is an 'imaginary' MUST which covers the entire procedure
from 5.5.3 (a) through (e).

If this is the intent, and the original text was not very clear for
many others, we might add to 2462bis something like:

5.5.3  Router Advertisement Processing

   A host configured to create global addresses using Router
   Advertisements MUST perform the followings for each
   Prefix-Information option in the Router Advertisement:

BTW: the following part of Section 5.5 may have some relevant point:

   Creation of global and site-local addresses and configuration of
   other parameters as described in this section SHOULD be locally
   configurable. However, the processing described below MUST be enabled
   by default.

With the deprecation of site-local addresses and ignoring the "other
parameters" part, it reads:

  "Creation of global addresses SHOULD be locally configurable."

I'm not 100% sure what "locally configurable" means, but I think this
generally controls whether the node performs entire 5.5.3 or doesn't
perform any part of 5.5.3 at all, rather than allowing finest-grained
flexibility, e.g., whether or not follow some specific part of the
rules such as 5.5.3 a.  If there is ambiguity here also, we may have
to fix it 2462bis.

> Is there a reason to prefer one of these two ways of precluding the use
> of autonomous address-configuration?  Is there a problem with using
> technique (1)?

One possible issue is how the hosts know on-link prefixes then.  They
can still rely on routers and (optionally) redirects, but it's not
really efficient.

					JINMEI, Tatuya
					Communication Platform Lab.
					Corporate R&D Center, Toshiba Corp.
					[email-masked]

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---

From: "Eric Klein" <[email-masked]>
Date: Wed, 2 Nov 2005 07:24:16 +0200

----- Original Message -----
From: "JINMEI Tatuya
> rules such as 5.5.3 a.  If there is ambiguity here also, we may have

I am concerned that when we depreciated site-locals that we may have left
similar holes in many RFCs.

Is there a procedure where we (as a working group) can go back and modify
these already approved RFCs and replace them with an indication that it is
updated (say a letter to indicate that it the most recent one) rather than
having corrections listed in several newer RFCs or assigning it a new number
or going through a lengthy last call procedure where other issues might
arise?

Eric

---

From: Fred Baker <[email-masked]>
Date: Wed, 2 Nov 2005 08:00:42 -0800

There are notes that can be put on RFCs. However, I should think that  
since site-local was deprecated later, this could be left to the next  
revision without ambiguity.

> or going through a lengthy last call procedure where other issues  

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