Technical Refresher Session 3

Overview Difference between communication between devices on a single logical network and communication between different logical networks. Role of a router/gateway in such a set of logical networks. Available protocols Exercises: Static routes Using OSPF

Routing basics Routing: How networks discover what paths they can use to send data packets. Best route goals can include: Shortest hops Fastest links Route around network failure

The role of the router Sits at connection point between networks. Primary functions: Send information to correct destination Send information ONLY to correct destination and nowhere else (save network resources)

Within a logical network Machines are physically connected via switches or hubs Each device has a Layer 2 MAC address -- associated with Layer 3 IP address using Address Resolution Protocol Network address and mask define boundaries of logical network

Between logical networks All traffic routed via default gateway Rules that determine where gateway sends packet = routes A route is a tuple specifying: Destination network (address/mask pair) Gateway (IP address)

Exercise 1: Static Routes Simulate a single ISP using static routes throughout its network

Dynamic Routing Static routing doesn’t scale beyond a couple of devices – 36 routes in this network! If edge routers can exchange information: only 9 routes needed. So, networks need a way to distribute routes between routers: OSPF and iBGP!

Exercise 2: Dynamic Routing Dynamic routing using OSPF See detailed notes in handout