Subject: RE: [nemo] comments on "Tree Discovery" draft

From: "Pascal Thubert \(pthubert\)" <[email-masked]>
Date: Wed, 25 Aug 2004 17:55:31 +0200

Hi Fan :)

Thanks for your interest. 2 high level points here:

1) I provide some (sometimes the obvious) response your questions inline
but my understanding is that what you really want is more clarity in the
doc. So thanks for your points and I'll go revisit the text for version
01. 

2) TD is a proposed solution for issue 24. One question is whether
people feel that this is a real important issue for NEMO, whether its RO
only, whether we need to do anything here at all. I'd appreciate your
point of view on this.

> 
> I have read the "Nested NEMO Tree Discovery" draft and have some
> comments as follows.
> 
> 1. In section 1, "if loops are avoided, the nested NEMO assumes the
> shape of a tree." It is not clear to me which one is described here,
> the real topology of nested nemo or the abstract model of that
topology?

You're right. It's the NEMO abstraction that's a tree. 

> What relationship between MRs is represented by the edge in the
"tree"?

TD as described is for nemo basic; as such, MRs form a single primary
careof that they use for registration. So a node is attached to another
one if it formed its primary careof from it and installed it as its
default gateway.

> In the multihoming nested nemo, the topology of NEMO is not a tree. I
think
> a Directed Acyclic Graph <N, E> where N is a set of nodes
> and E is a set of directed links is a more general model. MR and/or
> LFN/VMN
> belongs to E and there is a directed link from i to j, i->j as long as
j
> achieves the care of address from i.

Multihoming makes the picture more complex. We could limit to a set of
overlapping trees rooted at the various exits. We could also form DAGs
as you suggest. If -as I expect- you direct them towards the exits, that
would be overlapping DAGS, one per root-MR. The TIO can help build that
as well.

You could also imagine one DAG per nested MR and reverse DAG forwarding
to get out, but that will be much harder to set up, maybe using a link
state manet. 

Anyway this is way too much for nemo basic :)

> 
> 2.In the first papragraph in section 3.1, it seems to me that there is
no
> direct connection with the following text. Maybe delete it?

It justifies the need for multihoming and the next paragraph explains
that in the nested case, he router selection draft is not enough....

> 3. The draft descibes the state transitions in section 5.3. A state
machine
> diagram will be helpful.

OK

> 4. This draft proposes to use the RA message to carry TIO.
> I wonder how to pretect and verify those messages?
> A black hole attack is easily launched.

Right. Do you think that the usual suspects (L2 access control, SeND...)
are either insufficient or inappropriate? 

Pascal

---

From: Alexandru Petrescu <[email-masked]>
Date: Wed, 25 Aug 2004 19:23:11 +0200

Pascal Thubert (pthubert) wrote:
> people feel that this is a real important issue for NEMO, whether its
>  RO only, whether we need to do anything here at all. I'd appreciate 
> your point of view on this.

I doubt the name Tree Discovery fits.  I'd call it Tree Building (like
in team building) or something.  In a graph topology there's no tree to
be discovered but rather a sort of virtual tree to be overlayed over the
existing graph.  And, speaking of which, I'm sure OSPF builds spanning
trees, which may even be minimal.

Which leads me to offer my humble point of view replying to your
request: investigate instead the use of OSPF within an aggregation of
moving networks.  Which raises the question: why not.

> 4.  The Nemo ClusterHead of a tree exposes the tree in the RA/TIO and
>  MRs propagate the TIO down the tree with the RAs that they forward 
> over their ingress links.

Does this mean somehow that the "deeper" the tree the larger  size the
"leaf" RA's will be (because including many many TIO's)?

IMHO...

Alex

---

From: Alexandru Petrescu <[email-masked]>
Date: Wed, 25 Aug 2004 19:35:54 +0200

Pascal Thubert (pthubert) wrote:
> You could also imagine one DAG per nested MR and reverse DAG
> forwarding to get out, but that will be much harder to set up, maybe
> using a link state manet.

YEs, wouldn't a link-state manet help with all this tree discovery
stuff?  Especially with the A in DAG, i.e. avoiding loops?

> Anyway this is way too much for nemo basic :)

I agree,

Alex