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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 downloadUsing the tftpdnld Command
The tftpdnld command downloads a Cisco IOS software image from a remote server into Flash memory using TFTP.
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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=valueAfter you specify the variables， you must reenter the tftpdnld command. For example：
rommon 1 》 tftpdnldrommon 2 》 IP_ADDRESS=172.15.19.11rommon 3 》 IP_SUBNET_MASK=255.255.255.0rommon 4 》 DEFAULT_GATEWAY=172.15.19.1rommon 5 》 TFTP_SERVER=172.15.20.10rommon 6 》 TFTP_FILE=/tftpboot/c2600-i-mzrommon 7 》 TFTP_VERBOSE=1rommon 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=1Invoke 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.