Re: [Mip6] Issue 73: v4 mapped address in IPv6 header

[Koshiro MITSUYA <[e-mail]>]

Hello Hesham,


> Mapped addresses are supported in all major OSs (with the exception  
> of KAME)

Can you please explain what do you mean by "supported"?

We can use mapped addresses inside a node with KAME, but KAME rejects  
a packet
which has a mapped address as the source or destination address.

regards,
Koshiro



On 2007/02/26, at 12:07, Hesham Soliman wrote:

>
> Folks,
>
> This is the final issue listed on the tracker. This one is a bit long.
>
> Issue Text:
> -----------
>
> the IPv4 mapped address has a special meaning by RFC
> 2553 API.  It is not preferable to use the mapped address in IPv6
> headers (See the following the drafts)
> 	draft-itojun-v6ops-v4mapped-harmful
> 	draft-cmetz-v6ops-v4mapped-api-harmful
>
> In our code based on KAME, the IPv6 implementation discard a IPv6
> header which has the v4 mapped address for sanity at ip6_input() and
> ip6_rthadr2().  We also need to add the mapped address in an address
> list (the list of all addresses which the node has) to receive the
> header.  This is somehow uncomfortable because the mapped address is
> actually not routable.
>
>> From Hesham:
> => No one suggested that it should/would be routable. It's simply
> used to keep the packet format. There is no routing based on this
> information.
>
>> From Koshiro:
> => I am not sure whether it's just an implementation issues.  But  
> putting
> the mapped address in the address list in order to process the DSMIP
> IPv6 header means the mapped address may be chosen as a source address
> even the address is actually not routable.  To avoid this, we need
> e.g. an additional flag to distinguish the mapped address from others.
> I think some implementers will not accept this.
>
> The above is not only the reason again the mapped address in the IPv6
> header.  Please refer the draft-*-harmful.  So, my idea is to put HoA
> in IPv6 header and kind of IPv4 CoA option to idicate it's IPv4 CoA.
>
> BTW, if you just want to keep the packer format, I think it's better
> to use compatible address, or 6to4 address, or newly-defined address
> for this purpose.
>
> Analysis:
> ---------
>
> The resons listed in the issue text (and other reasons discussed in  
> the DT)
> as well as their rebuttal are listed in this section. The first  
> reason for
> using a different address format was that the use of mapped address  
> was not
> recommended. The issue text refers to two drafts above. Those two  
> drafts
> were discussed several years ago in 2002 (first v6ops meeting). The  
> only
> issue that was agreed on in those drafts was that the mapped  
> address should
> not be used as a routable address. Therefore, the issue  
> misinterprets the
> agreement in the community. Also, the mapped address is not used as a
> routable address in DSMIP. The drafts referred to above did suggest  
> the
> removal of the v4 mapped address altogether from IPv6, but this  
> suggestion
> was rejected and the drafts were not adopted. Mapped addresses are  
> supported
> in all major OSs (with the exception of KAME).
>
> The issue text also suggests the use of a different address format
> (compatible address, 6-to-4, or a new address format). The compatible
> address format was deprecated from the IPv6 address architecture  
> and the
> mapped format is the recommended format for embedding IPv4  
> addresses in
> IPv6. 6-to-4 addresses imply a specific tunnelling behaviour  
> (tunnelling to
> the v4 address), which is not useful for our purposes. A new  
> address format
> will be no different from the mapped address, which is designed for  
> this
> purpose.
>
> Another concern that was raised against the use of the mapped  
> address was
> that they are "implicit" in nature ad do not explicitly show the IPv4
> address. However, IP stacks must check the src address in the  
> packet to
> insure that is in fact a legal address (e.g. not multicast) in  
> ip6_input.
>
>
> Recommendation:
> --------------
>
> My recommendation is to reject this issue for several reasons:
> a. There is no clear problem with the current format, i.e. what  
> breaks?
> b. We've already removed the alt-CoA option in a previous issue, so  
> if we
> accept this issue we'd have to introduce a new address format for  
> DSMIP.
> This can take a long time and will yield the same result. Although,  
> if there
> is something specific in the mapped address format that will cause  
> problems,
> and a new address format will solve this problem then I'm  
> personally ok with
> the new address format. However, we need to understand what that  
> problem is.
>
>
>
> Regards,
> Hesham
>
>
>
>
>
>
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