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.

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