Subject: Re: New "IP Version 6 Addressing Architecture" draft

From: Bob Hinden <[email-masked]>
Date: Fri, 28 Jul 2000 14:03:21 -0700

Jack,

>During w.g. last call, I suggested a change of wording in the
>definition of IPv4-mapped addresses (mail attached below).  I
>see the suggestion was not incorporated in addr-arch-v3-01.
>Let me offer an example of what motivated my suggestion.

I did read and consider your suggestion.  I should have gotten back in touch.

>Suppose we have 2 IPv6/IPv4 nodes: Node A has IPv6 address A::A
>and IPv4 address 1.2.3.4.  Node B has IPv6 address B::B and IPv4
>address 5.6.7.8.  Node A is running a server which is listening
>for both IPv4 and IPv6 connections on an AF_INET6 socket.  A client
>on node B connects to node A's IPv4 address (1.2.3.4), with packets
>sourced from B's IPv4 address (5.6.7.8).  (Why does the client use
>A's IPv4 address?  Perhaps it is an AF_INET application that has
>not yet been upgraded, or perhaps the user entered 1.2.3.4.)  The
>server on node A accepts the connection, and because it is using
>AF_INET6 sockets, accept() returns B's IPv4 address as ::FFFF:5.6.7.8.
>In this example, an IPv4-mapped address (::FFFF:5.6.7.8) is used
>to represent the address of an IPv6/IPv4 node (B).
>
>Is this correct usage of IPv4-mapped addresses?  Or is it a violation
>of the architecture?

It is not the intended use of IPv4-mapped addresses, but I am not sure it 
is a violation of the architecture either.  From an protocol view, I don't 
think it is possible for a node to tell if it is talking to an IPv4 only 
node or an IPv4/IPv6 node.  They have separate identities.

I am not widely enthusiastic about making this change.  If folks think it 
is necessary, I think it would be better to change it to:

      This address is used to represent the addresses of IPv4 nodes
      as IPv6 addresses.

instead of listing the exceptions one by one.

Comments...

Bob

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From: Mauro Tortonesi <[email-masked]>
Date: Sat, 29 Jul 2000 12:38:16 +0200 (CEST)

> >Is this correct usage of IPv4-mapped addresses?  Or is it a violation

after a careful reading of rfc2553 i guess it is just the correct usage. 

-- 
Aequam memento rebus in arduis servare mentem...

Mauro Tortonesi			[email-masked]
Ferrara Linux User Group	http://www.ferrara.linux.it
Project6 - IPv6 for Linux	http://project6.ferrara.linux.it