Re: [MEXT] Last Call: draft-ietf-mext-nemo-pd (DHCPv6 Prefix Delegation for NEMO) to Proposed Standard

[Alexandru Petrescu <[e-mail]>]

Le 09/09/2010 08:01, Hesham Soliman a écrit :
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> On 9/09/10 3:54 PM, "Wassim Haddad"<[e-mail]>
> wrote:
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>> On Sep 8, 2010, at 7:58 AM, Alexandru Petrescu wrote:
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>>> I agree mainly with the document draft-ietf-mext-nemo-pd.
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>>> It is good and needed to dynamically assign a Mobile Network
>>> Prefix to the NEMO-enabled Mobile Router.
>>>
>>> However, here are a couple of missing points.
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>>> One missing point is about how will the Mobile Router configure
>>> its default route on the home link?  I thought Prefix Delegation
>>>  would bring DHCP in the picture and would allow MR to synthesize
>>>  a default route even though RAs are absent.  But I now realize
>>> that a DHCPv6-PD implementation (and std?) does not allow a
>>> router (MR) to synthesize its default route (neither RA does, nor
>>> DHCPv6-nonPD does).
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> =>  I think the MR can easily act as a host on its egress interface
> and configure its default/next hop router that way. Of course the
> other alternative is to use routing protocols, but I think using ND
> should be sufficient.

Hesham - when at home, the MR acts  as a router (ip_forward==1,
join all-routers group), as such ND is insufficient to obtain the
default route - it's a Router.

When at home, and using DHCPv-PD, the MR also acquires its Home Address
with DHCPv6.  If so, then it doesn't use SLAAC to auto-configure neither
a Home Address nor a default route.

In implementation it is of course possible to dynamically change MR
behaviour from Host to Router: be at home, first act as host (fwd==0) to
acquire the Home Address and default route, then set fwd=1 and use
DHCPv6-PD to acquire a prefix (but not the Home Address) and take
advantage of the default route acquired previously as a Host.  This is
one way of solving the issue.  However it is not specified.  I am not
sure how clean is it anyways to disregard that 'M' bit of RA anyways.

The alternative to using routing protocols (OSPF?) to communicate a
default route to the MR - I am not sure how this could work, never seen
it in practice.

Alex


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> Hesham
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