Lecture 7 : Routing (Feb 10)

Todays instruction was focused on how Routing works. It is important to understand the difference between the terms forwarding or routing. Forwarding is used when describing a packet at one hop, while routing is in reference to the whole path taken by a packet. There were two major types of connections discussed, Virtual Connections and Datagram Networks. Virtual Connections are technologies such as ATM, Frame Relay, and X2.5. These methods create a connection from end to end. This allows ATM to guarantee no loss, order, timing and rate of data transfer. Virtual Connections are efficient and practical in smaller network models, but fail in larger networks because resources are tied up in reserved connections. Datagram Networks, on the other hand, are much more efficient with large-scale networks. IP is the Datagram network protocol. There is not dedicated connection from one client to the other. The data is forward from one device to the next until it reaches the destination. IP cannot make any of the guarantees that ATM could, but it keeps the networks simple and fast. Next the lecture focused on the basics of how a forwarding table works. Forwarding tables have assigned IP address ranges that correspond to a routers interface locally. If an IP address falls within a certain range, the packet would be sent on that interface. A common method used in forwarding tables is longest prefix matching. This means that the forwarding table entry that matches the most digits in the IP address will correspond to the interface that the data will be sent on.