(Reposted from the bears online, thank Johnh)
When we get a new router, we usually use any configuration files, this file we usually referred to as config, generally there is NVRAM. The operating system of the router is called iOS, and there is a flash. When the router is started for the first time, since there is no config file, the router will prompt "Notice: NVRAM INVALID, POSSIBLY DUE TO WRITE ERASE.", Then start a Wizard process, configure it in a dialog. Of course, general professionals skip this process and use them directly with the command line. It is to be pointed out that most of the Cisco network devices are configured with the command line mode CLI, and there is no intuitiveness of the Windows graphical interface. If the current configuration is selected after the conversation mode is configured, the router stores the configuration into the NVRAM, and we can use the command SH confs in privileged mode. Thereafter, the router will be initialized by the configuration file in NVRAM when the router is started, and the conversation configuration interface will not appear again. If you want to use a dialog configuration again, you must clear the current profile, command is ERA Start, pay attention to not be knocking with the wrong parameters, otherwise you may delete iOS, the router can not start. After deleting the configuration, you need to restart, the command is REL, if the system prompts if the configuration is saved, it should be selected (otherwise equal to not deleting). 2. The router access method and several modes. The debug router can generally connect to the console port of the router with a computer's serial port, running Windows HyperterMinal or other compatible serial communication programs. The general serial port is set to a rate of 9600 kbps, and the port characteristics are 8-N-1. Alternatively, you can use the network connection to access through Telnet, and the conditions are of course the Ethernet or WAN port of the computer to the router is UP. If the port Down will, if you don't have to say it? Connect to the router in a variety of ways, see the interface called user mode User Mode, can run some simple commands in this mode, view the status of the router, but cannot see or modify the router configuration. To write configuration, you must enter privileged mode, or called global mode, command is EN. After entering the privileged mode, the system's prompt will also change accordingly. In privileged mode we can view configuration, router status and set the following router parameters. When we are configured by the router, you must use the conf t command to enter the global configuration mode. In the configuration of a network interface, a line, a controller, or a routing protocol, there is also a respective port configuration mode, a line configuration mode, a controller configuration mode, and a routing configuration mode. 3. According to the several patterns mentioned above, there should be various access control passwords to ensure security. The last few lines on the above configuration file is a password set for different access lines. For example, VTY 0 4 specifies that the Telnet mode can have 0 to 4 total 5 lines to access the router simultaneously, and login specifies that the user must access the password when the user is logged in, and inputs 123 can enter. The password setting of the line is only for the user mode, that is, if you connect from the console port to the router, after entering the password 123, only enter the user mode, the configuration file is not seen. Want to change the configuration? Enter the command EN, because there is a line of en pass 456 above the configuration file, the system will ask the password of your privilege, and enter 456 will enter the privilege mode. Such a general user can log in to the router even if you know the access password, because there is no privileged mode password, it cannot be modified.
