CCNA 1 and 2 Companion Guide, Revised (Cisco Networking Academy Program) part 71 doc

Summary 669 Summary In this chapter, you learned the following key points: ■ The default source for Cisco IOS Software depends on the hardware platform, but, most commonly, the router looks to the configuration commands saved in NVRAM. ■ You can use the show version command to display information about the Cisco IOS Software version that is currently running on the router. ■ You can enter multiple boot system commands to specify the fallback sequence for booting Cisco IOS Software. Routers can boot Cisco IOS Software from Flash memory, from a TFTP server, and from ROM. ■ You use the show flash command to verify that you have sufficient memory on your system for the Cisco IOS Software that you want to load. ■ With Cisco IOS Software Release 11.2 and later, the naming convention for Cisco IOS contains the following three parts: — The platform on which the image runs — The special capabilities of the image — Where the image runs and whether it has been zipped or compressed ■ You can copy a system image back to a network server. This copy of the system image can serve as a backup copy and can be used to verify that the copy in Flash memory is the same as the original file. ■ If you need to load the backup Cisco IOS Software version, you can use a varia- tion of the copy command, copy tftp flash, to download the image that you pre- viously uploaded to the TFTP server. To supplement all that you’ve learned in this chapter, refer to the chapter-specific Videos, PhotoZooms, and e-Lab Activities on the CD-ROM accompanying this book. 1102.book Page 669 Tuesday, May 20, 2003 2:53 PM 670 Chapter 14: Managing Cisco IOS Software Key Terms bootstrap The protocol used by a network node to determine the IP address of its Ethernet interfaces to affect network booting. Flash memory A special type of EEPROM that can be erased and reprogrammed in blocks instead of one byte at a time. Many modern PCs have their BIOS stored on a Flash memory chip so that it can be updated easily if necessary. Such a BIOS is some- times called a Flash BIOS. Flash memory is also popular in modems because it enables the modem manufacturer to support new protocols as they become standardized. NVRAM (nonvolatile random-access memory) RAM that retains its contents when a unit is powered off. RAM (random-access memory) Volatile memory that can be read and written by a microprocessor. RCP (remote copy protocol) Protocol that allows users to copy files to and from a file system residing on a remote host or server on the network. TFTP (Trivial File Transfer Protocol) Simplified version of FTP that allows files to be transferred from one computer to another over a network, usually without the use of client authentication (for example, username and password). Check Your Understanding Complete all the review questions to test your understanding of the topics and con- cepts in this chapter. Answers are listed in Appendix C, “Check Your Understanding Answer Key.” 1. Which of the following correctly describes a method for specifying how a router loads the Cisco IOS software? A. Designate fallback sources for the router to use in sequence from NVRAM. B. Configure the Cisco IOS Software image for the location where it will bootstrap. C. Manually boot a default system image at a virtual terminal. D. Manually boot a default system image at the network server. 1102.book Page 670 Tuesday, May 20, 2003 2:53 PM Check Your Understanding 671 2. Which of the following is not a boot option that can be set with the configura- tion register boot field? A. Cisco IOS Software boots in ROM monitor mode. B. Cisco IOS Software automatically boots from ROM. C. Cisco IOS Software automatically boots from a TFTP server. D. NVRAM is examined for boot system commands. 3. Which of the following is information displayed by the show version command? A. Detailed statistics about each page of the router’s memory B. The name of the system image C. The names and sizes of all files in Flash memory D. The status of configured network protocols 4. Which command is used to discover the configuration register setting? A. show register B. show running-config C. show version D. show startup-config 5. What information is not provided in the Cisco image filename system? A. The capabilities of the image B. The platform on which the image runs C. Where the image runs D. The size of the image 6. Which of the following is not part of the recommended procedure for loading a new Cisco IOS Software image to Flash memory from a TFTP server? (The pro- cedures are listed in correct order.) A. Back up a copy of the current software image to the TFTP server. B. Enter the copy flash tftp command to start downloading the new image from the server. C. The procedure asks if you are willing to erase Flash memory. D. A series of Vs on the display indicates successful checksum verification. 1102.book Page 671 Tuesday, May 20, 2003 2:53 PM 672 Chapter 14: Managing Cisco IOS Software 7. What is the initial boot attempt if the router configuration register is set to 0x101? A. Setup mode B. TFTP server C. ROM D. Flash memory 8. Which of the following has a limited version of router Cisco IOS Software? A. ROM B. Flash memory C. TFTP server D. Bootstrap 9. What is the initial boot attempt if the router configuration register is set to 0x102? A. Flash memory B. TFTP server C. ROM D. Check for boot system commands 10. Which of the following is the sequence used by the router for automatic fallback to locate the Cisco IOS Software? A. Flash memory, (2) NVRAM, (3) TFTP server B. NVRAM, (2) TFTP server, (3) Flash memory C. NVRAM, (2) Flash memory, (3) TFTP server D. TFTP server, (2) Flash memory, (3) NVRAM 11. Which of the following is not displayed by the Cisco IOS show version command? A. Statistics for configured interfaces B. The type of platform running the Cisco IOS Software C. The configuration register setting D. The Cisco IOS Software version 1102.book Page 672 Tuesday, May 20, 2003 2:53 PM Check Your Understanding 673 12. Which of the following correctly describes preparing to use a TFTP server to copy software to Flash memory? A. The TFTP server must be a connected router or a host system, such as a UNIX workstation or a laptop computer. B. The TFTP server must be a system connected to an Ethernet network. C. The name of the router containing the Flash memory must be identified. D. The Flash memory must be enabled. 13. Why do you create a Cisco IOS Software image backup? A. To verify that the copy in Flash memory is the same as the copy in ROM B. To provide a fallback copy of the current image before copying the image to a new router C. To create a fallback copy of the current image as part of the procedures dur- ing recovery from system failure D. To create a fallback copy of the current image before updating with a new version 14. What is the command you need to issue if you want to upgrade an old version of the Cisco IOS Software by downloading a new image from the TFTP server? A. boot system tftp 131.21.11.3 B. copy tftp flash C. show flash D. tftp ios.exe 1102.book Page 673 Tuesday, May 20, 2003 2:53 PM Objectives Upon completion of this chapter, you will be able to ■ Understand routing basics ■ Describe routed and routing protocols ■ Describe interior and exterior protocols ■ Describe static versus dynamic routes ■ Configure static routes ■ Configure default routes ■ Troubleshoot static route configurations ■ Describe why dynamic routing protocols are necessary ■ Describe distance vector routing ■ Describe link-state routing ■ Understand how to use different routing protocols in context 1102.book Page 674 Tuesday, May 20, 2003 2:53 PM Chapter 15 Routing and Routing Protocols In this chapter, you learn more about the router’s use and operations in performing the key internetworking function of the Open System Interconnection (OSI) reference model’s network layer, Layer 3. In addition, you review the difference between routing and routed protocols and how routers track distance between locations. Finally, you learn more about distance vector, link-state, and hybrid routing approaches and how each resolves common routing problems. Please be sure to look at the e-Labs, Videos, and PhotoZooms associated with this chapter that you will find on the CD-ROM accompanying this book. These CD elements are designed to supplement the material and reinforce the concepts introduced in this chapter. Routing Basics Path determination for traffic going through a network cloud occurs at the network layer (Layer 3). The path-determination function enables a router to evaluate the available paths to a destination and to establish the preferred handling of a packet. Routing services use network topology information when evaluating network paths. This information can be configured by the network administrator or can be collected through dynamic processes running in the network. The network layer provides best-effort end-to-end packet delivery across interconnected networks. The network layer uses the IP routing table to send packets from the source net- work to the destination network. After the router determines which path to use, it proceeds with forwarding the packet. The router forwards the packet that it accepted on one inter- face to another interface or port that reflects the best path to the packet’s destination. Routing is the process that a router uses to forward packets toward the destination net- work. A router makes decisions based upon the destination IP address of a packet. All devices along the way use the destination IP address to point the packet in the correct 1102.book Page 675 Tuesday, May 20, 2003 2:53 PM 676 Chapter 15: Routing and Routing Protocols direction. The destination IP address enables the packet to eventually arrive at its des- tination. To make the correct decisions, routers must learn the direction to remote net- works. When routers use dynamic routing, the direction to remote networks is learned from other routers. When static routing is used, a network administrator configures information about remote networks manually. Because static routes must be configured manually, any network topology changes require the network administrator to add and delete static routes to account for the changes. In a large network, this manual maintenance of routing tables could require a tremendous amount of administrative time. On small networks with very few possible changes, static routes require very little maintenance. Static routing does not have the scalability of dynamic routing because of the extra administrative requirements. However, even in large networks, static routes that are intended to accomplish a very specific purpose often are configured in combination with a dynamic routing protocol. Although dynamic routing protocols can determine automatically routes, they still must be acti- vated initially and configured by a network administrator to accomplish this. The sections that follow cover various routing concepts: ■ The process of routing packets from source to destination ■ Addressing ■ Path selection and packet switching ■ Routed and routing protocols How Routers Route Packets from Source to Destination To be truly practical, a network must consistently represent the paths available between routers. As Figure 15-1 shows, each line between the routers has a number that the routers use as a network address. These addresses must convey information that can be used by a routing process to pass packets from a source toward a destination. Using these addresses, the network layer can provide a relay connection that interconnects independent networks. The consistency of Layer 3 addresses across the entire internetwork also improves the use of bandwidth by preventing unnecessary broadcasts. Broadcasts invoke unneces- sary process overhead and waste capacity on any devices or links that do not need to receive the broadcasts. By using consistent end-to-end addressing to represent the path of media connections, the network layer can find a path to the destination without unnecessarily burdening the devices or links on the internetwork with broadcasts. 1102.book Page 676 Tuesday, May 20, 2003 2:53 PM Routing Basics 677 Figure 15-1 Network Addresses Network and Host Addressing The router uses the network address to identify the destination network of a packet within an internetwork. Figure 15-2 shows three network numbers identifying seg- ments connected to the router. Figure 15-2 Network Addresses with Host Portions Most network protocol-addressing schemes use some form of host or node address. For some network layer protocols, a network administrator assigns network host addresses according to a predetermined internetwork addressing plan. For other net- work layer protocols, assignment of host addresses is partially or completely dynamic. In Figure 15-2, three hosts share the network number 1. 1 3 4 5 6 7 8 9 10 11 2 1.1 3.1 2.1 Network 1 2 3 1 2 3 1 1 Host 1.2 1.3 1102.book Page 677 Tuesday, May 20, 2003 2:53 PM 678 Chapter 15: Routing and Routing Protocols Path Selection and Packet Switching A router generally relays a packet from one data link to another using two basic functions: ■ A path-determination function ■ A switching function Figure 15-3 illustrates how routers use addressing for these routing and switching functions. The router uses the network portion of the address to make path selections to pass the packet to the next router along the path. The switching function allows a router to accept a packet on one interface and for- ward it through a second interface. The path-determination function enables the router to select the most appropriate interface for forwarding a packet. The node portion of the address is used by the final router (the router connected to the destination network) to deliver the packet to the correct host. Figure 15-3 How Routers Use Addressing for Routing and Switching Functions Routed Protocols Versus Routing Protocols Because of the similarity of the two terms, confusion often exists regarding the routed protocol and the routing protocol (see Figure 15-4). The following provides some clarification: ■ Routed protocol—Any network protocol that provides enough information in its network layer address to allow a packet to be forwarded from one host to another host based on the addressing scheme. Routed protocols define the field formats within a packet. Packets generally are conveyed from end system to end system. A routed protocol uses the routing table to forward packets. The Internet Proto- col (IP) is an example of a routed protocol. 1.1 1.0 2.0 3.0 3.1 2.1 Destination Network 1.0 2.0 3.0 Direction and Router Port 1.1 2.1 3.1 1102.book Page 678 Tuesday, May 20, 2003 2:53 PM . addresses is partially or completely dynamic. In Figure 15 -2, three hosts share the network number 1. 1 3 4 5 6 7 8 9 10 11 2 1. 1 3 .1 2 .1 Network 1 2 3 1 2 3 1 1 Host 1. 2 1. 3 11 02. book Page 677. example of a routed protocol. 1. 1 1. 0 2. 0 3.0 3 .1 2 .1 Destination Network 1. 0 2. 0 3.0 Direction and Router Port 1. 1 2 .1 3 .1 110 2. book Page 678 Tuesday, May 20 , 20 03 2: 53 PM . tftp 13 1. 21 . 11. 3 B. copy tftp flash C. show flash D. tftp ios.exe 11 02. book Page 673 Tuesday, May 20 , 20 03 2: 53 PM Objectives Upon completion of this chapter, you will be able to ■ Understand routing