Subject: [MEXT] Question about use of HoA destination option by an MN/MR when sending to the HA

From: Carlos Jesús Bernardos Cano <[email-masked]>
Date: Fri, 18 Jun 2010 19:01:05 +0200

Hi folks,

One simple question: for data packets sent by an MN/MR to its HA, it is
needed to include the HoA dst option? I'd say that it is not (RFC
3775bis states that this is only used in RO mode), but I wanted to
confirm it.

Thanks,

Carlos

-- 
Carlos Jesús Bernardos Cano     http://www.netcoms.net
GPG FP: D29B 0A6A 639A A561 93CA  4D55 35DC BA4D D170 4F67

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From: "Laganier, Julien" <[email-masked]>
Date: Tue, 22 Jun 2010 15:39:35 -0700

Hi Carlos -

We've discussed a related point earlier, i.e. whether to use RH2 when HA sends traffic locally generated to the MN and it seems that for the purpose of end-to-end communication between the MN and the HA, the HA is acting as a correspondent node and thus these communications can be considered as route optimized. 

For the specific case of MN sending traffic to the HA, following this excerpt of 3775bis, the MN will use a Home Address option:

   Route Optimization

      This manner of delivering packets does not require going through
      the home network, and typically will enable faster and more
      reliable transmission.

      The mobile node needs to ensure that a Binding Cache entry exists
      for its home address so that the correspondent node can process
      the packet (Section 9.3.1 specifies the rules for Home Address
      Destination Option Processing at a correspondent node).  The
      mobile node SHOULD examine its Binding Update List for an entry
      which fulfills the following conditions:

      *  The Source Address field of the packet being sent is equal to
         the home address in the entry.

      *  The Destination Address field of the packet being sent is equal
         to the address of the correspondent node in the entry.

      *  One of the current care-of addresses of the mobile node appears
         as the care-of address in the entry.

      *  The entry indicates that a binding has been successfully
         created.

      *  The remaining lifetime of the binding is greater than zero.

      When these conditions are met, the mobile node knows that the
      correspondent node has a suitable Binding Cache entry.

      A mobile node SHOULD arrange to supply the home address in a Home
      Address option, and MUST set the IPv6 header's Source Address
      field to the care-of address which the mobile node has registered
      to be used with this correspondent node.  The correspondent node
      will then use the address supplied in the Home Address option to
      serve the function traditionally done by the Source IP address in
      the IPv6 header.  The mobile node's home address is then supplied
      to higher protocol layers and applications.

--julien

> -----Original Message-----
> From: [email-masked] [mailto:[email-masked]] On Behalf Of
> Carlos Jesús Bernardos Cano
> Sent: Friday, June 18, 2010 10:01 AM
> To: [email-masked]
> Subject: [MEXT] Question about use of HoA destination option by an
> MN/MR when sending to the HA
> 
> Hi folks,
>

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From: Carlos Jesús Bernardos Cano <[email-masked]>
Date: Wed, 23 Jun 2010 09:28:30 +0200

Hi Julien,

On Tue, 2010-06-22 at 15:39 -0700, Laganier, Julien wrote:
> Hi Carlos -
> 
> We've discussed a related point earlier, i.e. whether to use RH2 when
> HA sends traffic locally generated to the MN and it seems that for the
> purpose of end-to-end communication between the MN and the HA, the HA
> is acting as a correspondent node and thus these communications can be
> considered as route optimized. 

I know a similar point was discussed in the past, and it's clear to me
that for packets sent by the HA to the MN/MR, the RH2 is used (though it
does not make much sense to me). However, for packets sent by the MN/MR
I think RFC3775bis is not clear about this. Section 11.3.1 talks about
the two possible modes (RO and BT), but it does not explicitly mention
that an MN/MR must use RO mode when communicating with the HA. I think
it is more consistent to make also the MN/MR follow RO operation when
sending packets (as the HA does), but this should be make more explicit
in RFC3775bis, otherwise implementers may interpret otherwise. Can we
add some text at in Section 11.3.1 similar to what is at the beginning
of Section 10.4.2? IMHO, it would help to clarify this.

Thanks,

Carlos

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From: "Laganier, Julien" <[email-masked]>
Date: Thu, 24 Jun 2010 09:42:52 -0700

Hi Carlos, all,

Carlos Jesús Bernardos Cano wrote:
> that for packets sent by the HA to the MN/MR, the RH2 is used (though
> it does not make much sense to me). However, for packets sent by the
> MN/MR I think RFC3775bis is not clear about this. Section 11.3.1 talks
> about the two possible modes (RO and BT), but it does not explicitly
> mention that an MN/MR must use RO mode when communicating with the HA.
> I think it is more consistent to make also the MN/MR follow RO
> operation when sending packets (as the HA does), but this should be
> make more explicit in RFC3775bis, otherwise implementers may interpret
> otherwise. Can we add some text at in Section 11.3.1 similar to what is
> at the beginning of Section 10.4.2? IMHO, it would help to clarify this.

I agree with you that it is more consistent, and my understanding is that it is also the recommended mode of operation; if you look at the excerpt below you will see that SHOULD is employed, and when a MN generates packets for its HA all of the conditions to use RO listed in the excerpt are met, as you can see below. Adding some text to Section 11.3.1 for clarification would clarify the situation, I agree. 

Another thing is, while reading in detail the text I've found something that's a bit unclear, see below:

[...]

> >       Address option, and MUST set the IPv6 header's Source Address field
> >       to the care-of address which the mobile node has registered

Above, having the home address in HOA option is a SHOULD, and setting the source address to the care-of address is a MUST. It's a bit ambiguous whether the second MUST is conditioned by the first SHOULD being followed, which I think should be the case. I'd like to suggest that we reword the first sentence as follows:

"A mobile node SHOULD arrange to supply the home address in a Home Address option. If the mobile node does so, it MUST set the IPv6 header's Source Address field to the care-of address which the mobile node has registered to be used with this correspondent node."  

What do people think?

--julien

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From: Carlos Jesús Bernardos Cano <[email-masked]>
Date: Fri, 25 Jun 2010 16:26:52 +0200

Hi Julien,

> I agree with you that it is more consistent, and my understanding is that it is also the recommended mode of operation; if you look at the excerpt below you will see that SHOULD is employed, and wh…

OK, I'll update the nemo-pd draft to be in-line with that.

> "A mobile node SHOULD arrange to supply the home address in a Home Address option. If the mobile node does so, it MUST set the IPv6 header's Source Address field to the care-of address which the mo…

I basically agree with your suggested change.

Thanks,

Carlos