Flash 被清空，只能进入rommon 模式，唯一办法重灌IOS镜像文件，所需IOS文件可以到cisco官方网站和www.net130.com下载：
    软件准备：
* 先找到与机型相配的IOS文件（注意机子的内存大小选择大小相配的文件）；
* 去下个Cisco TFTP Server；
   硬件准备：
* 除了要一根控制线外，还要一根交叉线来连接Router和你的控制电脑（注意Cisco Router一般规定了灌IOS必须用interface ethernet0/0，即第一个以太网端口）；
   注意事项：
* 你要灌的IOS文件要放到Cisco TFTP Server的根目录下，Cisco TFTP Server才会自动找到你所需要加载的IOS镜像文件；

通过concle口登录路由器，设置tftp的环境

rommon 1 >IP_ADDRESS=192.168.1.2                 //默认为路由器第一个以太网接口的ip

rommon 2 >IP_SUBNET_MASK=255.255.255.0    //设置路由器以太网接口的子网掩码

rommon 3 >DEFAULT_GATEWAY=192.168.1.1    //设置网关，否则tftp无法成功

rommon 4 >TFTP_SERVER=192.168.1.104           //设置笔记本ip，即为tftp server的ip

rommon 5 >TFTP_FILE=c2600-i-mz.123-6c.bin     //设置路由器要下载的ios文件名

rommon 6 > set                               //设置tftp完环境后，可以用set命令再检查一下，也可以略过

PS1=rommon ! >

RET_2_RTS=

IP_ADDRESS=192.168.1.2

IP_SUBNET_MASK=255.255.255.0

DEFAULT_GATEWAY=192.168.1.1

TFTP_SERVER=192.168.1.104

TFTP_FILE=c2600-i-mz.123-6c.bin

rommon 7 > tftpdnld                      //核对无误后，开始tftp

          IP_ADDRESS: 192.168.1.2
      IP_SUBNET_MASK: 255.255.255.0
     DEFAULT_GATEWAY: 192.168.1.1
         TFTP_SERVER: 192.168.1.104
           TFTP_FILE:c2600-i-mz.123-6c.bin

Invoke this command for disaster recovery only.
WARNING: all existing # in all partitions on flash will be lost!
Do you wish to continue? y/n: [n]: y

Receiving c2600-c-mz.121-9.bin from 192.168.1.104

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
File reception completed.
Copying file c2600-c-mz.121-9.bin to flash.
Erasing flash at 0x607c0000
program flash location 0x60120000

rommon 8 > confreg                   //下载ios完毕后，还需设置寄存器的值

      Configuration Summary
enabled are:
load rom after netboot fails
console baud: 9600
boot: image specified by the boot system commands
      or default to: cisco2-C2600

do you wish to change the configuration? y/n [n]: y      //要选择“y”
enable "diagnostic mode"? y/n [n]: n
enable "use net in IP bcast address"? y/n [n]: n
disable "load rom after netboot fails"? y/n [n]: n
enable "use all zero broadcast"? y/n [n]: n
enable "break/abort has effect"? y/n [n]: n
enable "ignore system config info"? y/n [n]: n
change console baud rate? y/n [n]: n
change the boot characteristics? y/n [n]: y      //要选择“y”
enter to boot:
0 = ROM Monitor
1 = the boot helper image
2-15 = boot system
    [2]:2                           //要选择“2”

    Configuration Summary
enabled are:
load rom after netboot fails
console baud: 9600
boot: image specified by the boot system commands
      or default to: cisco2-C2600

do you wish to change the configuration? y/n [n]:n

rommon 8 > reset                       //重启路由器

重启后，恢复正常

如果不能确定ios版本，可在路由器重启之前，按ctrl+break进入rommon后，输入reset命令，可以看到当前路由器需要ios的版本文件

本文来自CSDN博客，转载请标明出处：http://blog.csdn.net/yangfree990/archive/2010/06/10/5661937.aspx