Re: [Roll] updating DAO caches (was Re: Something to ADD)

[JP Vasseur <jvasseur at cisco.com>]

On Nov 17, 2009, at 5:12 PM, Richard Kelsey wrote:

> > From: Roger Alexander <roger.alexander at ekasystems.com>
> > Date: Mon, 16 Nov 2009 15:33:33 -0800
> >
> > Not clear why there is a need to know who records DAOs. In response  
> > to
> > a new child a parent that does maintain state will add itself to the
> > path information from the child and pass that information to it's
> > parent. That information will pass inward towards the root until a
> > node is encountered that can store the path information and  
> > previously
> > supported connectivity to the node at the same cost.
>
> The difficulty is that, at present, there is no way of
> determining how much information needs to be passed up after
> a move.  Here is the example I posted earlier.  We start
> with this, where A is the root:
>
>       A
>      / \
>     B   C
>     |
>     D
>     |
>     E
>
> Now D moves to C as its parent:
>
>       A
>      / \
>     B   C
>         |
>         D
>         |
>         E
>
> If only A caches DAO data, then all D needs to do is send a
> DAO after the move.  A receives it and changes its next hop
> for D and E to be C.

Well I think that you still need the no-DAO since A may continue to send
packets to D via both B and C.

> If B and C both cache DAO data, then D needs to send a
> no-DAO before the move, to update B, and both D and E need
> to send DAOs after the move, so that C knows that it has
> downward paths to both of them.

Note that with DAO packing only D will send one DAO for local prefixes
and E's prefixes but that's not the topic.

> In the first case a single DAO needs to be sent.  In the
> second case D has to send two DAOs and the nodes in its
> subdag, just E here, each need to send one.  If only the
> root caches DAOs then the first case always applies.  If
> other nodes may cache DAOs, then we have to assume that we
> are in the second case after every move.

Yes but I think that we need no-DAO to avoid nodes upper in the DAG to  
continue
to use an old path anyway and the issues of the number of DAO is IMO  
larger and
packing will sort it out.

>                            -Richard Kelsey
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