1. Technical Refresher Session 3

2. 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

3. 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

4. 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)

5. 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

6. 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)

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

8. 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!

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