Friday, August 08, 2008
If your Cisco router experiences difficulties and no longer contains a valid Cisco IOS software image in flash memory, you can download a new Cisco IOS image using one of the following ROM monitor commands:
§ Xmodem
§ Use this command to copy a Cisco IOS image from the console, if the computer attached to your console has a terminal emulator with Xmodem capability
§ The xmodem [filename]command establishes a connection between a console and the router console port for disaster recovery, if both the boot and system images are erased from flash memory.
§ Other options include the following:
§ c—Use cyclic redundancy check (CRC-16)
§ y—Use Ymodem transfer protocol
§ r—Copy the image to dynamic random-access memory (DRAM) for launch
§ x—Do not launch image on completion of download
§ Note: Downloading a Cisco IOS image from a console is very slow. This procedure should be used only in an emergency and is not recommended for normal Cisco IOS image upgrades
§ For the fastest possible download from a console, set the console speed to 115200 bps by using the confreg ROM monitor command
§ tftpdnld:
§ Use this command to copy a Cisco IOS image from a TFTP server that is accessible through the FastEthernet 0/0
§ Restrictions on the tftpdnld Command: Ethernet and FastEthernet accepts and sends only Ethernet V2.0 data packets
§ Note: The tftpdnld command is not available on the Cisco 2691 router
§ The recommended method for installing a Cisco IOS image on a Cisco 2691 router is from a Compact Flash memory card loaded in the external CompactFlash memory card slot
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Procedure for the xmodem Command |
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§ To copy a Cisco IOS image from a console to flash memory, perform the following procedure.
§ Note: File transfer from a console is slow and will take many minutes. |
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§ Step 1: Connect a console to the router's console port using the instructions in the "Connecting to a Console Terminal or Modem" section on page 3-20. |
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§ Step 2: Power up the router. The power-on self-test diagnostics run and the boot ROM searches for a valid boot image and Cisco IOS image in flash memory. If the boot image and Cisco IOS image are not found, the ROM monitor prompt is displayed:
§ rommon 1> |
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§ Step 3: Enter the xmodem command and the name of the source file containing the Cisco IOS image:
§ rommon 1> xmodem filename
§ When the source file is found, messages similar to the following appear: § Do not start upload program yet... § File size Checksum File name § 2537948 bytes (0x26b9dc) c2600-i-mz.122-10.bin § Note: This operation will ERASE bootflash. If the xmodem download to bootflash fails, you will lose any good image you may already have in bootflash. Invoke this application only for disaster recovery. § Do you wish to continue? [yes/no]: |
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§ Step 4: Enter yes to copy the Cisco IOS image into flash memory. Messages similar to the following appear: § Ready to receive file prog ... § Erasing flash at 0x3000000 § program flash location 0x3000000 § Transfer complete! |
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§ Step 5: The router is now ready to boot from the Cisco IOS image. Enter the reset ROM monitor command to reboot the router. |
Procedure for the tftpdnld Command |
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§ Step 1: Specify the required variables: § rommon 1> IP_ADDRESS=172.15.19.11 § rommon 2> IP_SUBNET_MASK=255.255.255.0 § rommon 3> DEFAULT_GATEWAY=172.16.19.1 § rommon 4> TFTP_SERVER=172.15.20.10 § rommon 5> TFTP_FILE=/tftpboot/c2600-i-mz |
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§ Step 2: Enter the tftpdnld [-h] [-r] command: § Options include the following: § h—Displays the tftpdnld command help screen. § r—Loads the Cisco IOS software image only to DRAM and launches the image without writing the image into flash memory. § rommon 6> tftpdnld § IP_ADDRESS=172.15.19.11 § IP_SUBNET_MASK=255.255.255.0 § DEFAULT_GATEWAY=172.16.19.1 § TFTP_SERVER=172.15.20.10 § TFTP_FILE=/tftpboot/2600-i-mz § Invoke this command for disaster recovery only. § WARNING: all existing data in all partitions on flash will be lost! § Do you wish to continue? y/n: [n]: |
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§ Step 3: Enter y to download the Cisco IOS software image. When the process is complete, the ROM monitor mode prompt appears on your screen. § rommon 7> |
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§ Step 4: The router is now ready to boot from the Cisco IOS image. Enter the reset ROM monitor command to reboot the router. |
Written by: Sarah Giard: Cisco Curricula Practice Owner, TEKsystems
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