Cisco Networking Academy Program CCNA 1 and 2 Companion Guide, Revised part 77 is the Cisco approved textbook to use alongside version of the Cisco Networking Academy Program CCNA 1 and CCNA 2 web-based courses. The topics covered provide you with the necessary knowledge to begin your preparation for the CCNA certification exam (640-801, or 640-821 and 640-811) and to enter the field of network administration. | Page 729 Tuesday May 27 2003 2 16 PM RIP Features 729 Example 16-4 show ip rip database Command Output Continued auto-summary 24 1 via 00 00 20 Serial0 0 This command outputs shows the last update was received 20 seconds ago. Observing Multiple Paths to Destination Some routing protocols support multiple paths to the same destination. Unlike single path algorithms these multipath algorithms permit traffic over multiple lines provide better throughput and are more reliable. RIP Features Routing Information Protocol RIP was originally specified in RFC 1058 in 1988. Its key characteristics include the following It is a distance vector routing protocol. Hop count is used as the metric for path selection see Figure 16-11 . If the hop count is greater than 15 the packet is discarded. By default routing updates are broadcast every 30 seconds. Note in Figure 16-11 that the path between the two hosts using the top routers is 2 hops. The lower alternate path using the three T-1 links is 4 hops. Because RIP path selection is based solely on the number of hops in this case RIP path selection chooses the link instead of the much faster T1 links. Figure 16-11 RIP Uses Hop Count as Its Metric Page 730 Tuesday May 27 2003 2 16 PM 730 Chapter 16 Distance Vector Routing Protocols RIP has evolved over the years from a classful routing protocol RIP Version 1 RIP-1 to a classless routing Protocol RIP Version 2 RIP-2 . RIP-2 enhancements include the following Capability to carry additional packet routing information Authentication mechanism to secure table updates Capability to support subnet masks RIP prevents routing loops from continuing indefinitely by implementing a limit on the number of hops allowed in a path from the source to a destination. The maximum number of hops allowed in a path is 15. When a router receives a routing update that contains a new or changed entry the metric value is .
