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3. Chapter III

3.9 Conclusion & Future Work

the kernel, we defined a new raw socket for interactions between the kernel and the daemon. If the kernel does not have an appropriate route for a destination, the kernel notifies the daemon through the raw socket to send RREQs across the ad hoc network.

Movement detection of Mobile IPv6 is triggered whenever the AODV6 dae-mon receives the new global IPv6 routable address. An IPv6 header includes the Home Address option and a Binding Update if it is needed. For implementations using a routing header, this requires use of two destination options after the routing header; more recently, the Binding Update has been modified to fit within a new header called the Mobility Header, but we have not yet implemented that new spec-ification. Most current IPv6 and Mobile IPv6 implementations on Linux cannot carry two destination options after the routing header owing to an implementation limitation. We therefore extended the LINUX IPv6 implementation to store both options after the routing header in the IPv6 header.

3.9. Conclusion & Future Work 61

In most cases, we have discovered that the necessary extensions are quite nat-ural. We have been able to formulate solutions for the above problems that work with the principal candidate routing protocols that are under consideration within the [Manet] (mobile ad hoc networks) working group of the IETF.

In our proposal, a Manet node with a need for global communication con-tacts an Internet Gateway by either sending a modified Router Solicitation, called Gateway Solicitation, or relying on a routing protocol route discovery functions.

When the gateway receives one of these messages, it unicasts a response back to the requesting node, specifying its globally routable prefix and IPv6 address. The node then uses this information to configure an address that is globally reachable throughout the Internet. With Mobile IPv6, the mobile node can use this address as its care-of address and make a Binding Update to its Home Agent.

When sending packets to the Internet, the node can either use a routing header specifying the Internet Gateway as the first destination and rely on ordinary ad hoc routing to route the packet to the gateway or send the packets through the default route, relying on intermediate nodes to forward the packet toward the destination.

Our AODV6 routing protocol implementation uses an extra flag, called the Internet-Global Address Resolution flag, so that the node-gateway signaling can work as efficiently as possible. Along the way we fixed certain parts of the Linux IPv6 implementation, work that may be useful in many other contexts. We have shown that it is possible to implement connectivity between ad hoc networks and the Internet, with only slight modifications to the existing specifications.

In the future, we would like to revisit the problem of selecting between mul-tiple Internet Gateways. In fact, it may be better to use mulmul-tiple gateways simul-taneously, depending on which one offers a shorter path to a particular Internet destination. This will require per-destination (or at least per-prefix) signaling. This is merely one instance of service selection for ad hoc networks, when a Manet node has the choice of several nodes offering a needed service.

We would also like to investigate ways to mark ad hoc networks as domains so that a mobile node could more easily distinguish between different ad hoc net-works. This may involve borrowing some relevant ideas from OSPF. Finally, we would like to consider the possibility of using an ad hoc network as a transit net-work for foreign traffic, where both the source and the destination nodes are al-lowed to lie outside the ad hoc network.

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