Getting Information About Remote Devices 639 The statistics reflect router operation since the last time the counters were cleared. Use the clear counters command to reset the counters to 0. By starting from 0, you get a better picture of the current status of the network. The show interfaces command can also be used to check the status of other interface types, such as Ethernet (E0), Fast Ethernet (Fa0), and Integrated Services Digital Network (ISDN) (BRI0). Checking Real-Time Traffic with the debug Command The router includes hardware and software to aid it in tracking down problems on it or on other hosts in the network. The debug privileged EXEC command starts the con- sole display of the network events specified in the command parameter. Use the termi- nal monitor command to forward debug output to your Telnet session terminal. Figure 13-10 displays the data-link broadcasts received by the router using the debug broadcasts command. Use the undebug all (or no debug all) command to turn off debugging when you no longer need it. Debugging is really intended for solving problems. Figure 13-10 Checking Real-Time Traffic with the debug Command By default, the router sends system error messages and output from the debug EXEC command to the console terminal. However, you can redirect messages to a UNIX host or to an internal buffer. The terminal monitor command enables you to redirect these messages to a terminal, which can be useful in cases where you use a UNIX or Linux host instead of the console terminal as a means of administering the devices. 22146 packets output, 2383680 bytes, 0 underruns 0 output errors, 0 collisions, 2 interface resets, 0 restarts 1 carrier transitions Example 13-6 show interfaces Command Output (Continued) CAUTION Be careful with the debug command on a live network. Substan- tial debugging on a busy network slows the network signifi- cantly. Do not leave debugging turned on; use it to diagnose a problem, and then turn it off. Excessive debugging on routers with minimal RAM can cause the router to force a reload. 1102.book Page 639 Tuesday, May 20, 2003 2:53 PM 640 Chapter 13: Learning About Neighboring and Remote Devices Summary In this chapter, you learned the following the key points: ■ CDP is a media- and protocol-independent, Cisco-proprietary protocol used for neighbor discovery. ■ CDP shows information only about directly connected neighbors. ■ You use CDP to show Layer 2 and 3 information about neighbors. ■ You should test network connectivity layer by layer. ■ Dealing with connectivity issues is the most common problem situation that occurs on IP networks. The following three commands are used to perform address-related troubleshooting: — ping uses the ICMP protocol to verify the hardware connection and the IP address of the network layer. This command is a very basic testing mechanism. — telnet verifies the application layer software between source and destina- tion. This command is the most complete test mechanism available. — traceroute allows the location of failures in the path from the source to des- tination. traceroute, or trace, uses TTL values to generate messages from each router along the path. 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. Lab Activity Troubleshooting IP Address Issues In this activity, you configure IP addresses for workstations and the test end-to- end network connectivity. 1102.book Page 640 Tuesday, May 20, 2003 2:53 PM Check Your Understanding 641 Key Terms CDP (Cisco Discovery Protocol) Used to obtain information about neighboring devices, such as the types of devices connected, the router interfaces they are connected to, the interfaces used to make the connections, and the model numbers of the devices. debugging To find and remove errors (bugs) from a program or design. ping Packet internet groper. ICMP echo message and its reply. Often used in IP networks to test the reachability of a network device. SNAP (Subnetwork Access Protocol) Internet protocol that operates between a network entity in the subnetwork and a network entity in the end system. SNAP specifies a standard method of encapsulating IP datagrams and ARP messages on IEEE networks. The SNAP entity in the end system makes use of the services of the subnet- work and performs three key functions: data transfer, connection management, and QoS selection. SNMP (Simple Network Management Protocol) Network management protocol used almost exclusively in TCP/IP networks. SNMP provides a means to monitor and control network devices, and to manage configurations, statistics collection, perfor- mance, and security. Telnet Standard terminal emulation protocol in the TCP/IP protocol stack. Telnet is used for remote terminal connection, enabling users to log in to remote systems and use resources as if they were connected to a local system. TLVs (Type Length Values) Blocks of information embedded in CDP advertisements. traceroute Program available on many systems that traces the path a packet takes to a destination. It is used mostly to debug routing problems between hosts. 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. What is a definition for telnet? A. A command to determine whether a specific IP address is accessible. It works by sending a packet to the specified address and waiting for a reply. B. A command that uses Time-To-Live (TTL) values to generate messages from each router used along the path. 1102.book Page 641 Tuesday, May 20, 2003 2:53 PM 642 Chapter 13: Learning About Neighboring and Remote Devices C. A command used to verify the application layer software between source and destination stations. This command is the most complete test mechanism available. 2. What information does testing a network by using the show interfaces serial command provide? A. It displays line and data link protocol status. B. It displays how the router directs traffic across the network. C. It displays the path that packets follow across the network. D. It displays the names of routers on the network. 3. What information does the show cdp neighbors command provide for each CDP neighbor? A. Device identifiers B. Address list C. Port identifier D. All of the above 4. The show cdp interface command is used to display which of the following? A. The values of the CDP timers and the interface status B. The encapsulation used by CDP for its advertisement and discovery frame transmission C. The interface configuration of the neighboring routers D. Both A and B 5. Which of these is true for the output of the command show cdp entry [device name]? A. It displays all the Layer 3 addresses present in the neighbor router. B. It displays the value of neighbors that the router has. C. It displays the list of the device numbers of all the neighboring routers. D. It displays all the Layer 2 addresses on the interfaces of the neighbor router. 6. To display the information that is obtained both from the show cdp neighbors and show cdp entry [device name] commands, which of the following commands is used? A. show cdp neighbors detail B. show cdp interface entry C. show cdp neighbors entry D. show cdp details 1102.book Page 642 Tuesday, May 20, 2003 2:53 PM Check Your Understanding 643 7. What information is displayed by the show cdp neighbors command? A. Neighbor device ID B. Local port type and number C. Decremental holdtime value, in seconds D. All of the above 8. What four important pieces of information do you receive after issuing a ping command? A. The size and quantity of ICMP packets; the timeout duration; the success rate; and the minimum, average, and maximum round-trip times B. The size and quantity of ICMP packets; the MAC address; the success rate; and the minimum, average, and maximum round-trip times C. All of the above D. None of the above 9. What information does testing a network by using the traceroute command provide? A. It determines if the line protocol is operational. B. It determines if a routing table entry exists for the target network. C. It maps every router that a packet goes through to reach its destination. D. It determines if upper-layer applications are functioning properly. 10. In reply to the ping command, exclamation points (!) indicate which of these? A. The number of successful echos B. The number of unsuccessful echos C. The number of hops before reaching the destination D. All of the above 11. What is true of the router debug commands? A. The debug privileged EXEC command starts the console display of the net- work events specified in the command parameter. B. The undebug all command (or no debug all) turns off debugging. C. The buffer debug command is used to buffer the login. D. Both A and B. 1102.book Page 643 Tuesday, May 20, 2003 2:53 PM Objectives Upon completion of this chapter, you will be able to ■ Identify the stages of the router boot sequence ■ Determine how a Cisco device locates and loads Cisco IOS Software ■ Use the boot system command ■ Identify the configuration register values ■ Describe the process used to locate Cisco IOS Software ■ Describe the process and commands for creating and loading a software image and configuration file backup ■ Describe Cisco IOS Software naming conventions 1102.book Page 644 Tuesday, May 20, 2003 2:53 PM Chapter 14 Managing Cisco IOS Software This chapter examines the stages of the router boot sequence, including how the Cisco router locates and loads Cisco IOS Software. This chapter also introduces the boot system command and explains how the boot system command tells the router to boot up. Also, you learn how to use a variety of Cisco IOS Software source options and execute commands to load Cisco IOS Software onto the router, maintain backup files, and upgrade Cisco IOS Software. In addition, you learn about the functions of the configuration register and how to determine which version of the Cisco IOS Software image file you have. Finally, this chapter describes how to use a TFTP server as a software source for the Cisco IOS Software image and configuration files. Please be sure to look at this chapter’s associated e-Labs, Videos, and PhotoZooms 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. Stages of the Router Power-On/Boot Sequence A router initializes by loading the bootstrap, the operating system, and a configuration file. If the router cannot find a configuration file, then it enters setup mode. The router stores a backup copy of the new configuration from setup mode in nonvolatile random- access memory (NVRAM). Figure 14-1 shows the events that occur as the router initializes. 1102.book Page 645 Tuesday, May 20, 2003 2:53 PM 646 Chapter 14: Managing Cisco IOS Software Figure 14-1 Router Startup Sequence The goal of the startup routines for Cisco IOS Software is to start the router opera- tions. The router must deliver reliable performance in connecting to the user networks it was configured to serve. To do this, the startup routines must do the following: 1. Make sure that the router loads ROM. 2. Find and load the Cisco IOS Software image that the router uses for its operating system. 3. Find and apply configuration statements, including protocol functions and inter- face addresses. When a Cisco router powers up, it performs a power-on self test (POST). During this self test, the router executes diagnostics from ROM on all hardware modules. These diagnostics verify the basic operation of the CPU, memory, and network interface ports. After verifying the hardware functions, the router proceeds with software initialization. Locating and Loading Cisco IOS Software The default source for Cisco IOS Software startup depends on the hardware platform. However, the router usually looks to the boot system commands saved in NVRAM. Cisco IOS Software does, however, allow you to use several alternatives. You can spec- ify that the router look at other sources for software. Also, the router can use its own fallback sequence, as necessary, to load the software. Figure 14-2 illustrates how the Cisco IOS Software image is located. 1102.book Page 646 Tuesday, May 20, 2003 2:53 PM Locating and Loading Cisco IOS Software 647 Figure 14-2 Locating Cisco IOS Software The settings in the configuration register enable the following alternatives: ■ You can specify global configuration mode boot system commands to enter fall- back sources for the router to use in sequence. When the router restarts, it uses these commands in sequence as needed. ■ If NVRAM does not have boot system commands that the router can use, the system uses the Cisco IOS Software in Flash memory by default. ■ If Flash memory is empty, the router next attempts to use Trivial File Transfer Protocol (TFTP) to load a Cisco IOS Software image from the network. The router uses the configuration register value to form a filename from which to boot a default system image stored on a network server. ■ If a TFTP server is unavailable, the router will load the limited version Cisco IOS Software image stored in ROM. Using the boot system Command You can enter multiple boot system commands to specify the fallback sequence for booting Cisco IOS Software. Examples 14-1, 14-2, and 14-3 show boot system entries that specify that a Cisco IOS Software image will load first from Flash memory, then from a network server, and finally from ROM. Configuration Registers Registers in NVRAM for Modifying Fundamental Cisco IOS Software; Identifies Where to Boot Cisco IOS Image (For Example, Use config mode Commands) Router# configure terminal Router(config)# boot system flash IOS_filename Router(config)# boot system tftp IOS_filename tftp_address Router(config)# boot system rom [Ctr–Z] Router# copy running-config startup-config Boot System Commands Not Found in NVRAM Get Default Cisco IOS Software from Flash Flash Memory Empty TFTP Server Unavailable Get Limited Cisco IOS Software from ROM Get Default Cisco IOS Software from the TFTP Server 1102.book Page 647 Tuesday, May 20, 2003 2:53 PM 648 Chapter 14: Managing Cisco IOS Software The command copy running-config startup-config saves the commands in NVRAM. The router executes the boot system commands as needed and in the order in which they were originally entered into configuration mode. To see if any boot system com- mands have been entered, issue the show startup-config command. Booting from Flash Memory Booting from Flash memory involves loading a system image from electrically erasable programmable read-only memory (EEPROM). The advantage here is that information stored in Flash memory is not vulnerable to network failures that can occur when load- ing system images from TFTP servers. Example 14-1 specifies that the gsnew-image Cisco IOS Software file be loaded from Flash. Booting from a Network Server In case Flash memory becomes corrupted, a system image can provide a backup by specifying that it should be loaded from a TFTP server. Example 14-2 specifies that the test.ext image file be loaded from the TFTP server at IP address 172.16.13.111. Booting from ROM If Flash memory is corrupted and the network server fails to load the image, booting from ROM is the final bootstrap option in software. However, the system image in ROM will likely be a subset of Cisco IOS Software. This subset lacks the protocols, features, and configurations of full Cisco IOS Software. Also, if the software has been updated since the router was purchased, the router might have an older version of Cisco IOS Software. Example 14-3 demonstrates this last bootstrap option. Example 14-1 Booting from Flash Memory Router# configure terminal Router#(config)# boot system flash gsnew-image [Ctrl-Z] Router# copy running-config startup-config Example 14-2 Booting from a Network Server Router# configure terminal Router#(config)# boot system tftp IOS_image 172.16.13.111 [Ctrl-Z] Router# copy running-config startup-config 1102.book Page 648 Tuesday, May 20, 2003 2:53 PM . terminal Router#(config)# boot system tftp IOS_image 17 2 .16 .13 .11 1 [Ctrl-Z] Router# copy running-config startup-config 11 02. book Page 648 Tuesday, May 20 , 20 03 2: 53 PM . path. 11 02. book Page 6 41 Tuesday, May 20 , 20 03 2: 53 PM 6 42 Chapter 13 : Learning About Neighboring and Remote Devices C. A command used to verify the application layer software between source and. software. Figure 14 -2 illustrates how the Cisco IOS Software image is located. 11 02. book Page 646 Tuesday, May 20 , 20 03 2: 53 PM Locating and Loading Cisco IOS Software 647 Figure 14 -2 Locating Cisco