Lecture 7 Unicast Routing Protocols RIP OSPF and

Lecture 7 Unicast Routing Protocols: RIP, OSPF, and BGP Objectives Upon completion you will be able to: • Distinguish between intra and interdomain routing • Understand path vector routing and BGP Dr. Hussam Dheaa Kamel 1

7. 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 7. 1 Autonomous systems 3

Figure 7. 2 Popular routing protocols 4

7. 6 PATH VECTOR ROUTING Path vector routing is similar to distance vector routing. There is at least one node, called the speaker node, in each AS that creates a routing table and advertises it to speaker nodes in the neighboring ASs. . The topics discussed in this section include: Initialization Sharing Updating 5

Figure 7. 3 Initial routing tables in path vector routing 6

Figure 7. 4 Stabilized tables for four autonomous systems 7

7. 7 BGP Border Gateway Protocol (BGP) is an interdomain routing protocol using path vector routing. It first appeared in 1989 and has gone through four versions. The topics discussed in this section include: Types of Autonomous Systems Path Attributes BGP Sessions External and Internal BGP Types of Packets Packet Format Encapsulation 8

Figure 7. 5 Internal and external BGP sessions 9

Figure 7. 6 Types of BGP messages 10

Figure 7. 7 BGP packet header 11

Figure 7. 8 Open message 12

Figure 7. 9 Update message 13

Note: BGP supports classless addressing and CIDR. 14

Figure 7. 10 Keepalive message 15

Figure 7. 11 Notification message 16

Table 7. 3 Error codes 17

Note: BGP uses the services of TCP on port 179. 18