The IP protocol is the most common of the routed protocols. AppleTalk and Novell IPX still exist in some networks but are no longer as common as they were a few years ago. How does a routed protocol behave? Let’s examine an IP packet in our fictitious Sprockets corporate network.
In this example, an Intel PC controlling robot, on the manufacturing floor segment of the Sprockets’ network, will make a database query to an IBM mainframe host, on the data center network segment. The manufacturing segment media is fast Ethernet and the IBM host segment is on token ring. A layer 3 IP datagram will have traverse different layer 2 encapsulations and layer 1 media.
Both the IBM mainframe and the manufacturing floor robot controller are configured to use the layer 3 IP routed protocol. The IP datagram, originating in the controller PC, assigns the destination address of 123.21.3.47, the IP address of the IBM mainframe. The IP datagram is encapsulated in a layer 2 Ethernet frame and placed onto the wire. The beauty of the IP protocol is that a datagram doesn’t know how to directly get to its destination. This is the work of a routing protocol.
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