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

[Koshiro MITSUYA <[e-mail]>]

Hi Hesham,

Yes, KAME support it too with your meaning.
Can you revise this point?

I basically understand the analysis.
Thank you for the effort.

Koshiro



On 2007/02/26, at 16:14, Hesham Soliman wrote:

> Hi Koshiro,
>
>>> 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,
>
> => I meant at least what you describe above. So by my meaning I  
> guess KAME
> supports it too.
>
>    but
>> KAME rejects
>> a packet
>> which has a mapped address as the source or destination address.
>
> => Right, but as I mentioned below, I understand the reason for  
> doing that
> in general because it implies that there is no return address (in  
> the case
> of the src address), but this is not the case in DSMIP.
>
> Hesham
>
>>
>> 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
>>>
>>>
>>>
>>>
>>>
>>>
>>> _______________________________________________
>>> Mip6 mailing list
>>> [e-mail]
>>> https://www1.ietf.org/mailman/listinfo/mip6
>>
>>
>


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