Fault caused by router parameter error

About the router's fault there are many, many people do not understand its troubleshooting methods, the following to the network router for example, to introduce a more complex fault, this fault is representative.

First, the network router as a wide-area network backbone router, the network after the completion of the networking router 2M backbone Export line protocol in down state, so that with the network interruption, with "show running-config" command to check all the running parameters, no errors found; Show interfaces Serial "command to check the serial port, found that some ports state up, and the line protocol is down, and this situation is the serial port in the same serial board (a board), the other modules work properly.

All physical circuits are checked for normal, which eliminates the possibility of line failure. However, in general, the same as a serial port on the serial port at the same time the possibility of line failure is not large.

Two, to this point can be preliminary to determine the possibility of a plate out of the problem. When you enter the global configuration mode, and then want to enter the port on the A-board interface configuration mode is not implemented, each time you type "interface serial serial number", always error, but the same command can enter the port configuration mode of other ports. At this point, you can initially determine that iOS itself has some kind of software failure, with the reload command to restart the network after the system into the Rommonitor mode, prompt for "rommon>", type the command "boot" bootable network router but the fault still exists, And all the A-board serial configuration statements are all the error.

Thirdly, the network router is turned off and then the power is observed: Network router AC (or DC) OK LED light is green, this shows that the system's power supply subsystem is working properly, fan rotation is normal and output error LED lights are not lit, which indicates that the cooling subsystem is working properly, router processor (RSP) LED light is green, This also indicates that the system is working properly. The Enable LED light for each interface is green, indicating that RSP has completed the initialization of the interface processor.

But a board of LED lights flashed out, the implementation of the "reset" command and "boot" boot system after all the A-board serial configuration statements all disappeared.

Four, the further inspection of a board found that its model for VIP2, the two modules on the installation of only a four-string slot module, so a board only four strings (can be expanded to 8), of which three serial port has been used, an idle. Normal when the three use of the serial port LED lights should be bright, and not using the serial port LED lights should be yellow, but now is four serial port LEDs are not lit. After the system starts, use the command "show version" to discover that the system has found a board and identified the board model as VIP2, except for details.

Five, in the last line of display information, found that the network router configuration register value is 0x0, modify it to 0x2102, reboot the network router, the backup configuration from the Tftpserver into the Running-config, the network piece router work back to normal, This eliminates the seemingly defective hardware interface and is a failure to set the software parameter incorrectly. The network router register value is composed of four 16 binary digits, wherein the low 4 bits determine the startup mode of the system: when the minimum 4 digits are 0-0-0-0, the network router does not load the system mirroring, but enters the monitoring state (ROM Monitor mode) or maintenance state (Maintenance mode) requires manual booting, and when the minimum 4 bits are 0-0-0-1, the network router mounts the system mirrors found from the ROMs.

When the minimum 4 digits are 0-0-1-0 for 1-1-1-1, the network router mounts the operating system mirroring in the settings of the Boot system command in the boot configuration, and if this command is not set, mounts the operating system image from a system mirror on a default network server.

When the 6th bit is 1 o'clock, the configuration in the NVRAM is ignored when the network router starts up, which is what we need to notice.