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The default source for Cisco IOS Software depends on the hardware platform; most commonly, though, the router looks to the configuration commands that are saved in
NVRAM. Cisco IOS Software offers several alternatives. You can specify other sources where the router should look for software or the router uses its own fallback sequence as necessary to load software.
Settings in the configuration register enable alternatives for where the router will bootstrap Cisco IOS Software. You can specify enabled configuration-mode boot system commands to enter fallback sources for the router to use in sequence. Save these statements in NVRAM to use during the next startup with the command copy runningconfig startup-config . The router uses these commands as needed, in sequence, when it restarts. If NVRAM lacks boot system commands that the router can use, the system has its own fallback alternatives. The router falls back and uses the default Cisco IOS
Software image in Flash memory. If Flash memory is empty, the router tries its next
TFTP alternative. The router uses the configuration register value to form a filename from which to boot a default system image that is stored on a network server.
Cisco develops many versions of IOS. The IOS supports different types of hardware and features. To identify the different versions of IOS Cisco developed a naming convention.
The main fields in the naming convention are
ƒ
ƒ
ƒ
ƒ
Hardware Platform
Feature Set
File Format
Version Number
Concept Questions
Demonstrate your knowledge of these concepts by answering the following questions in the space that is provided.
Routers boot Cisco IOS Software from
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Flash
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TFTP server
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ROM (not full Cisco IOS)
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Multiple source options that provide flexibility and fallback alternatives
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1.
Explain the process by which a router locates Cisco IOS software.
The default source for Cisco IOS software depends on the hardware platform.
Most routers use the boot system commands saved in NVRAM. Cisco IOS software allows several alternatives to be used. Other sources can be specified for the software, or the router can use its own fallback sequence to load the software.
2.
Explain the configuration register.
3.
4.
5.
6.
The configuration register is a 16-bit register in NVRAM that is represented as 4 hexadecimal digits. The lowest four bits of the configuration register form the boot field. The order in which the router looks for system bootstrap information depends on the boot field setting in the configuration register.
Boot system commands may be added to the startup configuration to allow a fallback sequence in loading the IOS. What is the purpose of having different versions of IOS as a fallback?
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.
If the configuration register is set for 0x2101 the boot system commands in the startup configuration file will not be used. Explain why?
The IOS automatically boots from ROM. It boots the first image in Flash.
Compare and contrast the boot options for obtaining Cisco IOS Software: from Flash memory, from the network, and from ROM.
⇒
Set the configuration register value to 0x100 if you need to enter the ROM monitor (primarily a programmer’s environment). From the ROM monitor, boot the operating system manually by using the b command at the ROM monitor prompt. (This sets the boot field bits to 0-0-0-0.)
⇒
Set the configuration register to 0x101 to configure the system to boot automatically from ROM. (This sets the boot field bits to 0-0-0-1.)
⇒
Set the configuration register to any value from 0x102 to 0x10F to configure the system to use the boot system commands in NVRAM. This is the default. (This sets the boot field bits to between 0-0-1-0 and 1-1-1-
1.)
Describe the course of action the router will take if the Cisco IOS in flash is corrupted.
If the flash image is corrupt, a new IOS should be uploaded into the router.
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7. Describe the show version command and all the information it tells you.
The show version command displays information about the Cisco IOS Software version that is currently running on the router. This includes the configuration register and the boot field setting. This line shows the system image name:
System image file is "c4500-f-mz", booted via tftp from 171.69.1.129
In addition, the show version command displays information about the type of platform on which the version of Cisco IOS Software is currently running.
8. Describe the processes for creating a software image backup, upgrading the image from a network, and loading a software image backup?
⇒
Creating a software image backup:
You should copy a system image back to a network server. This copy of the system image can serve as a backup copy. Use the show flash command to learn the name of the system image file (xk09140z), and the copy flash tftp command to copy the system image to a TFTP server. The files can be renamed during transfer.
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The copy tftp flash command:
After you have a backup copy of the current Cisco IOS Software image, you can load a new image. You download the new image from the TFTP server by using the command copy tftp flash . This command begins by requesting the IP address of the remote host that will act as the TFTP server. Next, the prompt asks for the filename of the new Cisco IOS Software image. You need to enter the correct filename of the update image (as it is named on the TFTP server).
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How to load a software image backup:
If you need to load the backup Cisco IOS Software version, again use the copy command copy tftp flash , which will enable you to download the image that you previously uploaded to the TFTP server. After you enter the copy tftp flash command, the system prompts you for the IP address (or name) of the TFTP server. This can be another router serving ROM or Flash software images. The system then prompts you for the filename of the software image.
9. If the router is booted into ROM monitor, what commands are available?
When the router is running in ROM monitor mode, only a limited subset of the
Cisco IOS Software feature set is available. ROM monitor mode allows write operations to Flash memory and is used primarily to replace the Cisco IOS
Software image that is stored in Flash memory.
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10. List and describe the four parts of the Cisco IOS naming convention.
The fields include the hardware platform identification, the feature set identification, and the numerical release.
11.
List and describe the four parts the Cisco IOS file name c2600-js-l_121-3.bin.
•
C2600 = Hardware Platform (2600)
• js = Feature Set
•
1 = File format
•
121-3 = Version number
Vocabulary Exercise
Define the following terms as completely as you can. Refer to the online curriculum or
CCNA 2 Chapter 5 from the Cisco Networking Academy Program CCNA 1 and 2
Companion Guide , Revised Third Edition, for help.
Boot field -- The boot field of the configuration register determines the location to be used in loading Cisco IOS Software images.
Boot system -- When the router boots, it looks in the configuration file for a boot system statement.
Checksum --1) Method for checking the integrity of transmitted data. A checksum is an integer value computed from a sequence of octets taken through a series of arithmetic operations. The value is recomputed at the receiving end and compared for verification.
2) Calculated checksum of the header and data fields.
Configuration register --In Cisco routers, a 16-bit, user-configurable value that determines how the router functions during initialization. The configuration register can be stored in hardware or software. In hardware, the bit position is set using a jumper. In software, the bit position is set by specifying a hexadecimal value using configuration commands. copy command –
Editor’s Note: “Copy command” is only used with the commands below. copy flash tftp -- the Cisco IOS Software can be backed up to a TFTP server using the copy flash tftp command.
copy run tftp --Copies the running configuration to a TFTP server. copy run start --Copies the running configuration to NVRAM. copy start tftp --Copies the configuration in NVRAM to a TFTP server.
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5 copy tftp flash --Copies the IOS image from a TFTP server to flash memory. copy tftp start --Copies the IOS image from a TFTP server to NVRAM copy tftp run --Copies the IOS image from a TFTP server and loads it as the running configuration.
EEPROM --EPROM that can be erased using electrical signals applied to specific pins.
Feature set --The second part of the filename identifies the various features that the Cisco
IOS Software file contains. You can choose from many different features, and these features are packaged in “software images.” Each feature set contains a specific subset of
Cisco IOS Software features.
file format --The third part specifies if Cisco IOS Software is stored in Flash memory in a compressed format and if the Cisco IOS Software image is relocatable.
Flash -- 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 sometimes 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.
Hardware platform --The platform for which the IOS image is designed.
NVRAM- RAM that retains its contents when a unit is powered off.
Ping --Short for Packet Internet Groper or Packet Internetwork Groper, a utility to determine whether a specific IP address is accessible. It works by sending a packet to the specified address and waiting for a reply. Ping is used primarily to troubleshoot Internet connections.
ROM -- Nonvolatile memory that can be read, but not written, by the microprocessor.
ROM monitor -- The ROM monitor performs the bootstrap process and provides lowlevel functionality and diagnostics. The ROM monitor is used to recover from system failures and to recover a lost password.
TFTP Server -- A simplified version of File Transfer Protocol (FTP) that allows files to be transferred from one computer to another over a network.
UDP (User Datagram Protocol) --Connectionless transport layer protocol in the TCP/IP protocol stack. UDP is a simple protocol that exchanges datagrams without acknowledgments or guaranteed delivery, requiring that error processing and retransmission be handled by other protocols. UDP is defined in RFC 768.
Version number -- The fourth part of the IOS filename identifies the version number and release of Cisco IOS Software. As Cisco develops newer versions of Cisco IOS
Software, the numerical version number increases.
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Xmodem -- You can use the xmodem command from the ROMmon mode to restore a
Cisco IOS Software image from the PC.
Focus Questions
1. Why might there be different versions of router operating systems?
The OS is a vital and necessary piece of the routing process. It creates the framework for which the entire routing process is based on. Different versions of software are necessary (based on the needed technologies and improvements made to the software).
2. Where can routers boot Cisco IOS Software from?
3.
B. A TFTP server
C. Both a and b
The router cannot be configured to look elsewhere if Cisco IOS Software is not in Flash memory.
A. True
B. False
4.
5.
The configuration register is an n-bit register in NVRAM. What is the value of n?
A. 8
B. 16
C. 32
What command would you use to check the configuration register setting?
B. config-register
6. What does the first E in EEPROM stand for?
A. Erasable
B. Electronically
C. Enable
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7. Which component is not required by a router to operate correctly?
A. A configuration file
B. A valid Cisco IOS image
C. A DNS server
CCNA Exam Review Questions
The following questions help you review for the CCNA exam. Answers appear in
Appendix B, "CCNA 1 and 2 Exam Review Questions Answer Key."
1. Which of the following correctly describes a method for specifying how a router loads 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.
2. Which of the following is the sequence that the router uses for automatic fallback to locate Cisco IOS Software?
A. Flash, NVRAM, TFTP server
B. NVRAM, TFTP server, Flash
C. NVRAM, Flash, TFTP server
D. TFTP server, Flash, NVRAM
3. Which of the following does not describe configuration register settings for Cisco
IOS Software bootstrapping?
A. The order in which the router looks for system bootstrap information depends on the boot field setting.
B. You change the configuration register setting with the command configregister .
C. Use a hexadecimal number when setting the configuration register boot field.
D.
Use show running-config command to check the boot field setting.
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4.
5.
6.
7.
8.
9.
Which of the following information does the Cisco IOS Software show version command display?
A. Statistics about the router's memory
B. Name of the system image
C. Information about the Flash memory device
D. Status of configured network protocols
Which of the following commands is used to discover the configuration register setting?
A. show register
B. show running-config
C.
show version
D. show startup-config
Which of the following does not correctly describe a fallback option for booting
Cisco IOS Software?
A. Flash memory provides storage that is not vulnerable to network failures.
B. Loading Cisco IOS Software from a TFTP server is a good option if Flash memory becomes corrupted.
C.
The system image that is booted from ROM is usually a complete copy of Cisco IOS Software.
D. ROM might contain an older version of Cisco IOS Software.
Which of the following correctly describes preparing to use a TFTP server to copy software to Flash memory?
A. The TFTP server must be another router or a host system such as a
UNIX workstation or a laptop computer.
B. The TFTP host must be a system that is connected to an Ethernet network.
C. The name of the router that contains the Flash memory must be identified.
D. The Flash memory must be enabled.
Which of the following is not a step in preparing to copy software from a TFTP host to Flash memory?
A. Check the router to make sure you can see and write into Flash.
B. Verify that the router has sufficient room to accommodate Cisco IOS
Software.
C.
Use show ip route command to make sure you can access the TFTP server over the TCP/IP network.
D. Check the TFTP server to make sure you know the file or file space for the
Cisco IOS Software image.
Which of the following does not describe the procedure to verify sufficient room in Flash memory for copying software?
A. Use show flash command.
B. Identify the total memory in Flash, which is the available memory.
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C. Compare the available memory with the length of the Cisco IOS Software image to be copied.
D. If there is not enough available memory, you can try to obtain a smaller
Cisco IOS Software image.
10. How would you determine the size of the Cisco IOS Software image file on a
TFTP server?
A. Go to the Cisco website and consult the image file size table.
B. Type on your router.
C.
Type ls on the TFTP server.
D. Telnet to the TFTP server and issue a show files command.
11. Which of the following is the fastest way to make sure the TFTP server is reachable prior to trying to transfer a Cisco IOS Software image file?
A. Trace the TFTP server.
B. Ping the TFTP server.
C. Telnet to the TFTP server.
D. Call the TFTP server administrator.
12. Why do you need to determine the file size of the Cisco IOS Software image on the TFTP server before transferring it to your router?
A. To check that there is enough space in Flash to store the file.
B. To verify that the file is the correct Cisco IOS Software for your router.
C. To complete a trivial File Transfer Protocol (FTP) operation, the file size must be known.
D. To calculate the download time for the file and the amount of time that the router will be out of service.
13. What information is not provided in the Cisco IOS Software image filename system?
A. Capabilities of the image
B. Platform on which the image runs
C. Where the image runs
D. Size of the image
14. Which of the following is not part of the procedure for creating a Cisco IOS
Software image backup to a TFTP server?
A. Use show flash command to learn the name of the system image file.
B. Enter command to begin the copy process.
C. Enter the IP address of the router that is holding the image file.
D. Rename the file during transfer.
15. Why does an administrator create a Cisco IOS Software image backup?
A. To verify that the copy in Flash is the same as the copy in ROM
B. To provide a fallback copy of the current image prior to copying the image to a new router
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C. To create a fallback copy of the current image as part of procedures during recovery from system failure
D. To create a fallback copy of the current image prior to updating with a new version
16. Which of the following is not part of the procedure for loading a new Cisco IOS
Software image to Flash memory from a TFTP server? (The procedures are listed in correct order.)
A. Back up a copy of the current software image to the TFTP server.
B.
Enter copy flash tftp command to download the new image from the server.
C. The procedure asks if you are willing to erase Flash.
D. A series of Vs on the display indicates successful check run verification.
17. Which of the following is not part of the procedure for loading a backup Cisco
IOS Software image to Flash memory from a TFTP server? (The procedures are listed in correct order.)
A. Enter copy tftp flash command.
B. A prompt asks you for the IP address of the TFTP server.
C.
If a file with the same name exists in Flash memory, the file that is being copied automatically replaces it.
D. Enter reload command to boot up the router using the newly copied image.
18. What is the initial boot attempt if the router register is set to Ox2100?
A.
ROM monitor
C. ROM
D. Flash
19. What is the initial boot attempt if the router register is set to Ox2101?
C. ROM
D. Flash
20. What is the initial boot attempt if the router register is set to Ox2102?
C. ROM
D. Flash
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21. Which one of the following commands will boot a router while in ROM monitor mode?
C.
D. rommon5>boot flash:ios image name rommon17>boot system flash: ios image name
22. Which of the following is not a part of the Cisco IOS naming convention?
23. Which hardware platform is supported by the image named c2600-d-l-120-5.bin?
C. 2600
24. What feature set is supported by the image named c2600-d-l-120-5.bin?
A. IP only
B. Desktop
C. Binary
D. IP/IPX
Editor’s Note: This question was included in error. The answer to this question is not addressed in the CCNA 1 and 2 Companion Guide , Revised Third Edition.
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