Putting It All Together

Once all network nodes have an IP address, they can send data packets to the IP address of any other node. Through the use of routing and forwarding, these packets can reach nodes on networks that are not physically connected to the originating node. This process describes much of what “happens” on the Internet. This is illustrated in the following figure:

Figure 3.6: Internet networking. Each network segment has a router with two IP addresses, making it "link local" to two different networks. Packets are forwarded between routers until they reach their ultimate destination.

In this example, you can see the path that the packets take as Alice chats with Bob using an instant messaging service. Each dotted line represents an Ethernet cable, a wireless link, or any other kind of physical network. The cloud symbol is commonly used to stand in for “The Internet”, and represents any number of intervening IP networks. Neither Alice nor Bob need to be concerned with how those networks operate, as long as the routers forward IP traffic towards the ultimate destination. If it weren't for Internet protocols and the cooperation of everyone on the net, this kind of communication would be impossible.

Now that we have seen how packets flow on IP networks, let's look at a very specialized kind of IP network: an OLSR mesh.