Subject: RE: Deprecate the "IPv4-compatible IPv6 address"

From: "Gray, Eric" <[email-masked]>
Date: Wed, 16 Mar 2005 16:46:39 -0500

Margaret,

	Does listing it as "deprecated" have the effect of 
making it "reserved", or does it effectively free it up
for re-assignment?

--
Eric

-----Original Message-----
From: [email-masked] [mailto:[email-masked]]On Behalf Of
Margaret Wasserman
Sent: Wednesday, March 16, 2005 3:52 PM
To: Bob Hinden; [email-masked]
Subject: Re: Deprecate the "IPv4-compatible IPv6 address"

Hi Bob,

Should there also be an upate to the IANA considerations section 
asking IANA to list this allocation as deprecated?

Margaret

At 11:46 AM -0800 3/16/05, Bob Hinden wrote:
>Hi,
>
>At last weeks IPv6 session in Minneapolis, the working group reached 
>a consensus to deprecate the "IPv4-compatible IPv6 address".  This 
>email is to verify this consensus on the mailing list and to review 
>the proposed text to deprecate these address in the update to the 
>IPv6 Address Architecture document.  A proposed revision of Section 
>2.5.2 is include below.
>
>Please review and comment.
>
>Thanks,
>Bob
>
>----------------------------------------------------------
>
>2.5.5 IPv6 Addresses with Embedded IPv4 Addresses
>
>    Two types of IPv6 addresses are defined that carry an IPv4 address in
>    the low-order 32 bits of the address.
>
>    The first, termed an "IPv4-compatible IPv6 address", was defined to
>    assist in the IPv6 transition.  These addresses are now deprecated
>    because the current IPv6 transition mechanisms no longer use them.
>
>    The format of "IPv4-compatible IPv6 address" is:
>
>    |                80 bits               | 16 |      32 bits        |
>    +--------------------------------------+--------------------------+
>    |0000..............................0000|0000|    IPv4 address     |
>    +--------------------------------------+----+---------------------+
>
>    Note: The IPv4 address used in the "IPv4-compatible IPv6 address"
>    must be a globally-unique IPv4 unicast address.
>
>    New or updated implementations are not required to support this
>    address type.  Existing implementations and deployments may continue
>    to use these addresses.
>
>    A second type of IPv6 address which holds an embedded IPv4 address is
>    also defined.  This address type is used to represent the addresses
>    of IPv4 nodes as IPv6 addresses.  This type of address is termed an
>    "IPv4-mapped IPv6 address" and has the format:
>
>    |                80 bits               | 16 |      32 bits        |
>    +--------------------------------------+--------------------------+
>    |0000..............................0000|FFFF|    IPv4 address     |
>    +--------------------------------------+----+---------------------+
>
>
>----------------------------------------------------------
>
>
>
>
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---

From: Brian E Carpenter <[email-masked]>
Date: Fri, 18 Mar 2005 11:25:57 +0100

Eric asks a good question.

I think the chances that some implementers will choose to store
IPv4 addresses in IPv6-sized structures is 100%. So I am strongly
of the view that that the IPv4-compatible *format*, i.e. a ::/96
prefix, needs to be reserved and never allocated. Of course, it
should never appear on the wire.

This can be fixed in the IANA Considerations.

     Brian

---

From: Colm MacCarthaigh <[email-masked]>
Date: Fri, 18 Mar 2005 10:35:49 +0000

On Fri, Mar 18, 2005 at 11:25:57AM +0100, Brian E Carpenter wrote:
> I think the chances that some implementers will choose to store IPv4
> addresses in IPv6-sized structures is 100%. So I am strongly of the
> view that that the IPv4-compatible *format*, i.e. a ::/96 prefix,
> needs to be reserved and never allocated. Of course, it should never
> appear on the wire.

The current reservation is for the ::/8, which contains both :: and
::ffff/96, so does it actually matter?

Incidentally, there are situations in which :: can appear validly on the
wire (but only as a source address) - with MLD for example, and that's
contained within the /96 that you're talking about.

-- 
Colm MacCárthaigh                        Public Key: [email-masked]

---

From: Bob Hinden <[email-masked]>
Date: Fri, 18 Mar 2005 10:16:20 -0800

Brian,

>should never appear on the wire.

The current listing on the IANA registry pages for IPv6 address space ( 
http://www.iana.org/assignments/ipv6-address-space ) that covers these 
addresses is:

   IPv6 Prefix           Allocation              Reference      Note
   -----------           ----------              ---------      ----
   0000::/8              Reserved by IETF        [RFC3513]      [1]

   [1]  The "unspecified address", the "loopback address", and the IPv6
        Addresses with Embedded IPv4 Addresses are assigned out of the
        0000::/8 address block.

So to my thinking it is listed as "Reserved by IETF" now and won't be 
reused without the IETF giving some direction to the IANA.  Do think we 
need to do more than this?

Bob

---

From: Brian E Carpenter <[email-masked]>
Date: Mon, 21 Mar 2005 13:33:12 +0100

>   IPv6 Prefix           Allocation              Reference      Note

That is OK for me, but I think it needs to be noted in the IANA Considerations
that IANA is to keep it reserved.

     Brian

---

From: Bob Hinden <[email-masked]>
Date: Mon, 21 Mar 2005 10:02:26 -0800

Brian,

At 04:33 AM 03/21/2005, Brian E Carpenter wrote:
...
>that IANA is to keep it reserved.

I am not sure we need to tell the IANA to not do anything, but there is no 
harm done so I will add a note to the IANA Considerations to keep it reserved.

Thanks,
Bob