Subject: [rfc2462bis] a minor nit in creation of global addresses

From: JINMEI Tatuya / 神明達哉<[email-masked]>
Date: Thu, 09 Dec 2004 18:40:33 +0900

I've been editing a new version of rfc2462bis, mainly addressing AD
comments, and I found one minor issue in Section 5.5.3 (creation of
global addresses using RA):

According to rfc2462bis-06, step (d) of the procedure can be
represented as follows:

d-1 check whether the prefix in RA is equal to the prefix of an address
    stateless autoconfiguration in the address list
d-2 if not, do some sanity checks, and form an address by concatenating
    the prefix with the interface identifier
d-3 add the new address to the list

But what if an address identical which is not configured by stateless
autoconfiguration (i.e., either manually or by DHCPv6) happens to be
identical to the address being configured?  The check in d-1 cannot
detect this since it only checks the prefix of a
stateless-autoconfigured address (note that this restriction is one of
rfc2462bis clarifications based on the wg consensus).  A naive
implementation would configure duplicated addresses, which should not
be the appropriate behavior (I actually made this mistake in my
initial attempt of implementing rfc2462bis).

Original RFC2462 also seems to have this issue, while the point is
vaguer due to its own unclear wording.

Such conflict should be rare, but I believe it makes sense to note
this explicitly in rfc2462bis.  The appropriate behavior in this case
might also be controversial, but I think the natural reaction is to
simply avoid configuring the duplicate address.

So, I'd like to propose to revise the last paragraph of bullet (d) of
Section 5.5.3 from:

      If an address is formed successfully, the host adds it to the list
      of addresses assigned to the interface, initializing its preferred
      and valid lifetime values from the Prefix Information option.

to:

      If an address is formed successfully and the address is not yet in
      the list, the host adds it to the list of addresses assigned to
      the interface, initializing its preferred and valid lifetime
      values from the Prefix Information option.  Note that the check
      against the prefix performed at the beginning of this step cannot
      always detect the address conflict in the list.  It could be
      possible that an address already in the list, configured either
      manually or by DHCPv6, happens to be identical to the newly
      created address whereas such a case should be atypical.

Comments?

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

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From: JINMEI Tatuya / 神明達哉<[email-masked]>
Date: Fri, 10 Dec 2004 16:41:19 +0900

>>>>> On Thu, 09 Dec 2004 18:40:33 +0900, 
>>>>> JINMEI Tatuya <[email-masked]> said:

> global addresses using RA):

(snip)

>       created address whereas such a case should be atypical.

I've not seen any responses to the proposal.  I'll probably need to
wait for a while, but I'd rather to send this version as proposed
soon.  Of course, comments on this change for the new version of the
document will be welcome.

					JINMEI, Tatuya

---

From: Syam Madanapalli <[email-masked]>
Date: Fri, 10 Dec 2004 15:23:16 +0530

Hi Jinmei,

I am wondering whether you are talking about the duplicate address (/128) or
duplicate prefix. Let us say, you have an address configured using DHCP
with differe IID and if you are using SLAAC using differe IID but same
prefix; is this okay?

-Syam

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From: JINMEI Tatuya / 神明達哉<[email-masked]>
Date: Fri, 10 Dec 2004 19:54:19 +0900

>>>>> On Fri, 10 Dec 2004 15:23:16 +0530, 
>>>>> Syam Madanapalli <[email-masked]> said:

> with differe IID and if you are using SLAAC using differe IID but same

Yes, this should be okay (while DHCPv6 does not provide the "prefix"
of an address, so we can detect those two have the same "prefix" only
by applying the prefix of the SLAAC address to the DHCPv6 address).

					JINMEI, Tatuya

---

From: Vlad Yasevich <[email-masked]>
Date: Fri, 10 Dec 2004 14:43:13 -0500

Hi

Jinmei

I am not sure I very much like the statement: 
      " and the address is not yet in the list"

This requires an implementation of Stateless Autoconfig
to keep track of all addresses assigned to an interface
(even statically assigned ones)  and not just prefixes
from which an address is formed.  This seems like a new
requirement on Stateless Autoconfig.

The "Note" is fine to have, plus implementations should be
able to deal correctly with trying to configure the same
address twice.

-vlad

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From: JINMEI Tatuya / 神明達哉<[email-masked]>
Date: Mon, 13 Dec 2004 18:27:04 +0900

>>>>> On Fri, 10 Dec 2004 14:43:13 -0500, 
>>>>> Vlad Yasevich <[email-masked]> said:

> requirement on Stateless Autoconfig.

But RFC2462 already required that a host maintain a list of addresses
containing both autoconfigured and manually-configured addresses:

   A host also maintains a list of addresses together with their
   corresponding lifetimes. The address list contains both
   autoconfigured addresses and those configured manually.

So, I don't think this is a new requirement.

Additionally, RFC2462 noted that host configuration variables were
"conceptual" ones and the actual implementation could be different.
In that sense, the host implementation does not have to implement the
additional note in rfc2462bis using a "list" data structure.

(rfc2462bis will remove the note on the "conceptual" nature due to
clarification/simplification regarding host's variables, but I believe
the main point here still applies and is pretty obvious without the
explicit notice).

Does this address your concern?

					JINMEI, Tatuya

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From: Vlad Yasevich <[email-masked]>
Date: Mon, 13 Dec 2004 13:46:03 -0500

Jinmei

> Does this address your concern?

Thanks you.  Yes, this addresses my concern.

-vlad