Subject: Re: [manet] Default route (internet route) for global connectivity

From: "Anders Nilsson" <[email-masked]>
Date: Mon, 27 Feb 2006 19:39:02 +0100 (CET)

Hi all,

>2. Whether you use a tunnel (or a routing header) or rely on "routing
>coherence" imposes different requirements. The first solution is the
>easiest because you explicitly say via which gateway you want your
>packets to go through. The second solution requires a logical
>organization (e.g. prefix continuity) and it's more complex to setup but
>you don't need to introduce any forwarding indirection (which usually
>means changing or "hooking into" the kernel in order to setup the tunnel).

...

> Other issues also arise: for example, once you have a default
> route how would your
> reactive protocol behave ? Always try to discover first and use the
> gateway if it fails ?
>

Actually, draft-wakikawa-manet-globalv6-04.txt discusses this. If a
proactive protocol is used, you use the default route if route lookup
fails.
If a reactive protocol is used, I agree that it is a bit tricky to decide
what the optimum solution is. This problem is not directly linked to
whether a default route is used or not, but more to what addressing
scheme, or autoconf. scheme that is used as you mentioned above. If we
allow more than 1 prefix within the MANET we either some form of
subnetting solution, or as seems to be normally assumed, a flat hierarchy.
How do we know whether the destination is located within the MANET or
outside in the Internet. This is what draft-wakikawa says:

"whenever a node needs to send a packet it uses the following routing
algorithm:

    -  The node looks up its routing table for the destination node.  If
       it found the discovered route, it sends the packet towards the
       destination.  The internet route MUST NOT be selected as a route
       for the destination at this point.

    -  If not, the node MAY request a route for the destination node.

        1. If an internet route exists, the node MAY wait for the above
           route request.

        2. If an internet route does not exist, the manet node obtains a
           default route.

        3. If the manet node does not get any route, the node sets an
           route entry into the routing table with the destination node
           pointing towards the internet route.  Then the manet node
           uses the route to transmit the packet through the internet
           route.

    -  If the manet node gets a route for the destination, it sets a
       host route for the destination, and sends packets according to
       this route (not the internet route)."

/Anders

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