介绍两种恢复CISCO IOS的方法

如果您的路由器的flash因为意外丢失了IOS，您可以在ROM monitor commands模式下通过如下两种办法恢复:
　　
　　1) xmodem―Use this if the computer attached to your console has a terminal emulator that has xmodem capability.
　　2) tftpdnld―Use this if you have a TFTP server directly connected to the Ethernet 0 port.
　　
　　Using the xmodem Command
　　The xmodem 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.
　　xmodem [filename]―Establishes an xmodem connection between the console and the router. The optional parameter filename specifies the source file containing the Cisco IOS image.
　　Other options include the following:
　　　・-c―use cyclic redundancy check (CRC-16)
　　　・-y―use Ymodem transfer protocol
　　　・-r―copy the image to DRAM for launch
　　　・-x―do not launch image on completion of download
　　
　　Using the tftpdnld Command
　　The tftpdnld command downloads a Cisco IOS software image from a remote server into Flash memory using TFTP.
　　tftpdnld―Begins the TFTP copy command.
　　The following variables are required:
　　・IP_ADDRESS―The IP address for the router you are using.
　　・IP_SUBNET_MASK―The subnet mask for the router you are using.
　　・DEFAULT_GATEWAY―The default gateway for the router you are using.
　　・TFTP_SERVER―The IP address of the server from which you want to download the image file.
　　・TFTP_FILE―The name of the file that you want to download.
　　・The following variables are optional:
　　・TFTP_VERBOSE―Print setting. 0=quiet, 1=progress, 2=verbose. The default is 1.
　　・TFTP_RETRY_COUNT―Retry count for ARP and TFTP. The default is 7.
　　・TFTP_TIMEOUT―Overall timeout of the download operation in seconds. The default is 2400 seconds.
　　・TFTP_CHECKSUM―Performs a checksum test on the image. 0=no, 1=yes. The default is 1.
　　The syntax for specifying the variables is:
　　VARIABLE_NAME=value
　　
　　After you specify the variables, you must reenter the tftpdnld command. For example:
　　rommon 1 > tftpdnld
　　
　　rommon 2 > IP_ADDRESS=172.15.19.11
　　
　　rommon 3 > IP_SUBNET_MASK=255.255.255.0
　　
　　rommon 4 > DEFAULT_GATEWAY=172.15.19.1
　　
　　rommon 5 > TFTP_SERVER=172.15.20.10
　　
　　rommon 6 > TFTP_FILE=/tftpboot/c2600-i-mz
　　
　　rommon 7 > TFTP_VERBOSE=1
　　
　　rommon 8 > tftpdnld
　　
　　
　　　　 IP_ADDRESS=172.15.19.11
　　　　 IP_SUBNET_MASK=255.255.255.0
　　　　 DEFAULT_GATEWAY=172.15.19.1
　　　　 TFTP_SERVER=172.15.20.10
　　　　 TFTP_FILE=/tftpboot/2600-i-mz
　　　　 TFTP_VERBOSE=1
　　
　　Invoke this command for disaster recovery only.
　　WARNING: all existing data in flash will be lost!
　　Do you wish to continue? y/n: [n]:
　　
　　Enter y to begin downloading the Cisco IOS software image. When the process is complete, the ROM monitor mode prompt displays on your screen.