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Re: [MEXT] using MR-HA tunnel vs. combining BU // Re: WGLC for draft-ietf-mext-nemo-pd-01.txt

Hi Ryuji,

On 2008/12/11, at 17:45, Ryuji Wakikawa wrote:
I'd say the MR still sends a BU with the R-flag set and without the MNP option, which will be considered as registration in Implicit mode by the HA.
Implicit mode requires some mapping between a mobile network prefix and a mobile router. 

The DHCPv6 server will do such mapping. More below:


     Implicit:

        In this mode, the Mobile Router does not include a Mobile
        Network Prefix Option in the Binding Update.  The Home Agent
        can use any mechanism (not defined in this document) to
        determine the Mobile Network Prefix(es) owned by the Mobile
        Router and to set up forwarding for the Mobile Network.  One
We have an implementation of NEMO+DHCPv6PD, and here the "mechanism to determine the Mobile Network Prefix(es) owned by the Mobile Router" is a simple message from the DHCPv6 server to the HA that advertises the MNP/HoA pair to the HA.
This paragraph does not say that such information must be retrieved at the home registration (but actually this is stated later in the RFC :-) see below)
example would be manual configuration at the Home Agent mapping 
        the Mobile Router's Home Address to the information required
        for setting up forwarding for the Mobile Network.
As stated in the sentence, This is an example so it does not exclude DHCPv6PD.
In RFC3963, we didn't consider a MR who doesn't have any mobile network prefix sends BU with R-flag set. In implicit mode, if there is no prefix for the MR, HA will reject the BU 

From section 6.2:

[...]
  -  If there is no option in the Binding Update carrying prefix
information, the Home Agent uses manual pre-configured information to determine the prefixes assigned to the Mobile Router and to set 
      up forwarding for the Mobile Network.  If there is no information
that the Home Agent can use, it MUST reject the Binding Update and 
      send a Binding Acknowledgement with status set to 143 (Forwarding
      Setup failed).
[...]
In our implementation, at home registration the HA checks with the DHCP server if a prefix is available for this HoA. If so, registration is done (but not forwarding). Once the DHCPv6 server has delegated a prefix to the MR, it informs the HA that it can setup forwarding for the delegated MNP.
The RFC does not explicitely says that forwarding must be setup at home registration, but it says that the HA must check wether such information is available.
What is really missing in the NEMO DHCPv6PD draft is IMHO details on what (and how) the HA and DHCPv6 server need to agree. 

Cheers,
romain
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