拓扑图：
- 1 配置任意特权加密密码,并保存
Router>enable Router#config t Enter configuration commands, one per line. End with CNTL/Z. Router(config)#hostname R1 R1(config)#interface g 0/0 R1(config-if)#ip address 192.168.1.1 255.255.255.0 R1(config-if)#no shutdown R1(config-if)#enable secret asdf %LINK-5-CHANGED: Interface GigabitEthernet0/0, changed state to up R1(config)#exit R1# %SYS-5-CONFIG_I: Configured from console by console R1#wr Building configuration... [OK] R1#
- 2 重启路由器reload
- 3 在加载系统过程中， 使用 Ctrl+Break 键或者 Ctrl+C 键，修改 confreg寄存器的值，使路由器绕过配置文件进入系统
rommon 1 > help boot boot up an external process confreg configuration register utility dir list files in file system help monitor builtin command help reset system reset set display the monitor variables tftpdnld tftp image download unset unset a monitor variable rommon 2 > confreg 0x2142 rommon 3 > reset
- 4 此时已可以不输入密码即可进入系统，这时我们重新配置密码。配置密码完成后，修改confreg寄存器的值，引导系统正常启动。
Router>en Router#config t Enter configuration commands, one per line. End with CNTL/Z. Router(config)#hostname R1 R1(config)#enable sec R1(config)#enable secret 123abc R1(config)#config-register 0x2102 R1(config)#end R1# %SYS-5-CONFIG_I: Configured from console by console R1#wr Building configuration... [OK]
- 5 最后重启reload