Lecture 5 Unicast Routing Protocols RIP Objectives Upon

Lecture 5 Unicast Routing Protocols: RIP Objectives Upon completion you will be able to: • Distinguish between intra and interdomain routing • Understand distance vector routing and RIP Dr. Hussam Dheaa Kamel 1

5. 1 INTRA- AND INTERDOMAIN ROUTING Routing inside an autonomous system is referred to as intradomain routing. Routing between autonomous systems is referred to as interdomain routing. 2

Figure 5. 1 Autonomous systems 3

Figure 5. 2 Popular routing protocols 4

5. 2 DISTANCE VECTOR ROUTING In distance vector routing, the least cost route between any two nodes is the route with minimum distance. In this protocol each node maintains a vector (table) of minimum distances to every node The topics discussed in this section include: Initialization Sharing Updating When to Share Two-Node Loop Instability Three-Node Instability 5

Figure 5. 3 Distance vector routing tables 6

Figure 5. 4 Initialization of tables in distance vector routing 7

Note: In distance vector routing, each node shares its routing table with its immediate neighbors periodically and when there is a change. 8

Figure 5. 5 Updating in distance vector routing 9

Figure 5. 6 Two-node instability 10

Figure 5. 7 Three-node instability 11

5. 3 RIP The Routing Information Protocol (RIP) is an intradomain routing protocol used inside an autonomous system. It is a very simple protocol based on distance vector routing. The topics discussed in this section include: RIP Message Format Requests and Responses Timers in RIP Version 2 Encapsulation 12

Figure 5. 8 Example of a domain using RIP 13

Figure 5. 9 RIP message format 14

Figure 5. 10 Request messages 15

Example 1 Figure 5. 11 shows the update message sent from router R 1 to router R 2 in Figure 5. 8. The message is sent out of interface 130. 10. 0. 2. The message is prepared with the combination of split horizon and poison reverse strategy in mind. Router R 1 has obtained information about networks 195. 2. 4. 0, 195. 2. 5. 0, and 195. 2. 6. 0 from router R 2. When R 1 sends an update message to R 2, it replaces the actual value of the hop counts for these three networks with 16 (infinity) to prevent any confusion for R 2. The figure also shows the table extracted from the message. Router R 2 uses the source address of the IP datagram carrying the RIP message from R 1 (130. 10. 02) as the next hop address. See Next Slide 16

Figure 5. 11 Solution to Example 1 17

Figure 5. 12 RIP timers 18

Example 2 A routing table has 20 entries. It does not receive information about five routes for 200 s. How many timers are running at this time? Solution The 21 timers are listed below: Periodic timer: 1 Expiration timer: 20 − 5 = 15 Garbage collection timer: 5 19

Figure 5. 13 RIP version 2 format 20

Figure 5. 14 Authentication 21

Note: RIP uses the services of UDP on well-known port 520. 22