假如您的路由器的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.