Subject: [nemo] Questions and remarks on Home Network Models

From: Alexandru Petrescu <[email-masked]>
Date: Thu, 18 Nov 2004 15:05:40 +0100

Pascal, here are some new comments on the Home Network Models draft, 
especially on the section on Extended Home Networks.

Overall, I think I understand large parts of the draft and seem ok to 
me, but there are other small parts to which I don't agree, or maybe
reformulation may be needed.

What do you think?

> NEMO extends the concept of Home so that it is not only a flat subnet
>  composed of Home Addresses but an aggregation that is itself 
> subnetted in mobile and Home Networks.

This sounds interesting, so during all my reading I'm looking to
understand this concept.

> As an example, say that the aggregation has a global routing prefix 
> of m = 48 bits (A:B:C::/48), with subnet ID size of n = 16 bits ( n +
>  m = 64).
> 
> Say that a Mobile Router, MR1, owns the MNP A:B:C:1::/64: With NEMO 
> Basic Support, and depending on the deployment, MR1 may register 
> using a Home Address from the Home network, A:B:C:0::1, say, or a 
> Home Address, A:B:C:1::1, say, from one of its MNPs.
> 
> In a given deployment, one subnet may be reserved for the Home Link 
> (say A:B:C:0::/64) while the others are attributed to Mobile Routers 
> as Mobile Networks (as A:B:C:1::/64 for MR1).

I understand this.  Maybe in the last line you meant Mobile Network
Prefixes instead of Mobile Networks?

> Another approach could be to configure the Aggregation of Mobile 
> Networks as the subnet on the Home Link, and let the Mobile Routers 
> manage the overlapping networks.

Does this approach cover the case where the home link has RAs with /48
and the MNPs have each RAs with /64?  If this approach covers this case
then I agree with it.  Otherwise, I don't understand it.

Section 4 Extended Home Network:  I partially agree with this model to
work, see below.  However, I still do not understand why is it called
"Extended", what does it extend more exactly?  Is there a non-extended
home network model?

> o  The Home and the MNPs are tailored to allow for IPv6 Stateless 
> Address Autoconfiguration with typical interface identifier length 
> for the type of interface (can be for example /64).

Sidenote: a prefix advertised by RA should not necessarily be /64 in 
order for the address autoconf to work with IID /64.  The prefix in RA 
can also be /48 or anywhere between /48 and /64.  Implementations do 
this.  Do you agree with this?

> o  The prefix length of the Extended Home Network is shorter than 
> that of the Home Network and the MNPs, since it is an aggregation 
> (can be for example /48).

When I read this I think that maybe "Extended Home Network" should stand
for the Moving Networks, the Home Link _and_ the HA that acts as a
Gateway for that Home Link to the Internet, is it so?

> o  Alternatively, a Mobile Router could also form a Home Address from
>  one of its prefixes and use it to register, performing its own DAD 
> on its ingress network.

It is not clear to me how this can happen, I think it can not happen at 
all correctly.

Or maybe let's put it this way: maybe there is a form of Home Network, 
that is not extended, and where MR always uses a Home Address derived 
from the prefix on the home link, and not derived from its MNP.  I think 
such a deployment is easy to do.  If you agree with this, maybe this 
kind of Home Network deserves its own section, right before the section 
describing the Extended Home Network.  What do you think?

Alex