Flash and NVRAM key storage devices of Cisco Routers

Flash and NVRAM are two important storage devices for Cisco Routers: Flash and NVRAM, correct geographic understanding and understanding of its usage can better complete the configuration and management of routers. One pair of Flash maintenance www.2cto.com Flash is like the BIOS (Basic Input and Output System) on a PC, which stores the Cisco router IOS, the maintenance mainly involves the backup and recovery of IOS files. Run the "dir" command in the enable state of the vro to view the IOS file name and size stored in Flash. For example, for Cisco 1720 IOS, the file name is c1700-y-mz.120-4.T and the length is 2666496 bytes. Flash is a programmable memory. Therefore, you can compile Flash and upgrade IOS. You can also use erase flash to delete IOS in Flash. Therefore, you must be cautious when using this command. We can back up an IOS image file on the computer to fix IOS as needed. The computer used for backup should act as the TFTP Server, that is, it must run the software of the TFTP Server. For UNIX workstations, you only need to modify/etc/inetd. the conf file opens the TFTP service, and then runs "kill-1 [inetd process number]" to restart the inetd process. For Windows hosts, you only need to restart the Cisco TFTP Server http://soft.online.ha.cn Download) install it on your computer and run it. You can use it after setting the path of the TFTP root directory. TFTP is called Trivial File Transfer Protocol. Compared with FTP, FTP does not provide error correction control, password authentication, and other functions. However, before sending a file to the server, the other party must have the file and append it to the end of the existing file, if this file is not found on the server side, an error occurs. In general, we generate a file with the same name as the IOS file name on the TFTP server, but the length is zero bytes. After an empty file is generated using the touch command in UNIX, the access permission should be changed to 777. on a Windows host, you can create an empty text file and change it to a specified file, for example, for Cisco1720, the file name can be set to c1700-y-mz.120-4.T. There are two ways to operate a vro on www.2cto.com: connect the terminal to its console port and remotely log on (telnet ). The former is generic, and the latter is only applicable when the router LAN port has been correctly set. The TFTP used for IOS backup must run through the network. Therefore, even if the first method is used, the backup can be performed only when the LAN port is correctly set. After the TFTP server runs properly, a specified empty file is generated, and the vro LAN port is correctly set, type the copy network command on the vro to specify the IP address of the TFTP server, the IOS file can be transferred to the TFTP server. The TFTP server and the computer used to control the maintenance router may not be the same. If you accidentally use the "erase flash" command to delete the IOS vro, you can use its backup to restore it. Because the router cannot work normally after IOS is deleted, it cannot be transmitted via telnet. You can only use a microcomputer serial port to connect to the Console port of the router. For Windows super terminals, you need to pay attention to a problem, that is, generally set the serial port speed of the Console port of the router to 9600 bit/s, which is also the default router Console port rate. Because the IOS file is large and the transfer speed of 9600 bit/s is too long, you can use the "confreg" (set register) command to increase the Console port speed. Set the Console port speed to the highest 115200 bit/s as prompted. garbled characters may appear on the terminal screen because the serial port speed of the terminal is not changed to 115200 bit/s. Therefore, you only need to modify the serial port speed to 115200 bit/s, close the Super Terminal, and then re-open it. The garbled characters will disappear. After the router is started, it enters the ROM Monitor status. The "rommon>" command prompt appears on the terminal. At the "rommon>" prompt, type "xmodem". When "prepare to receive files" appears, select the "transfer" menu on the Super Terminal and click "Send file... "menu item, in the" Send File "window, select the file transfer protocol as" Xmodem ", and select the file to be sent, that is, the IOS file. Click "send" to send the IOS file to the vro. The router decompress the received file and write it to Flash. In this case, enter the "reset" command on the "rommon>" prompt to restart the vro. Then, you can call it to IOS and enter the "Automatic Configuration" status. Now, the ios of the vro is successfully restored. Two pairs of NVRAM maintenance NVRAM is like a CMOS on a PC, which stores the configuration parameters of the router. For NVRAM content, you can use "erase memory" or "write erase" to delete the configuration parameters to the factory settings. Therefore, the consequence of deleting NOVRAM is not serious when the IOS vro is lost, recovery is easier. After the vro starts normally, it copies the NVRAM content to the memory. Our vro setting is actually to modify the parameters in the memory. Therefore, the content in the memory and NVRAM can be different until you use "write memory" and "copy running-config startup-config" to save the memory settings to NVRAM, you can also use "reload", "copy startup-config running-config", or restart a vro to re-import NVRAM content to the memory to synchronize NVRAM with the memory. Run the "show configuration" command to view the settings in NVRAM. Run the "show running-config" and "write terminal" commands to view the currently running settings (in memory ). NVRAM can also be backed up. There are two backup methods: Screen Copy or write to the TFTP server. The Windows Super Terminal has a cache to save the previously displayed content. After executing the "show configuration" command on the vro, we can flip the window forward, copy the content displayed by this command to generate a text file, which enables NVRAM backup. When writing data to a TFTP server, a computer on the network is also required to act as a TFTP server, and the agreed NVRAM file name is generated in advance, and the "write network" command is executed on the router, specify the IP address of the TFTP server. The current NVRAM configuration of the vro will be saved to the root directory of the TFTP server as a file. If www.2cto.com accidentally deletes NVRAM content, the router enters the factory settings, and there are two ways to restore: Screen Copy or read from the TFTP server. Screen Copy is to use a text editor to open the previously backed up NVRAM file, select all the content, copy it to the clipboard, and paste it in the config state of the router, the vro executes each line of the pasted command. When reading data from a TFTP server, you must first ensure that the LAN port of the router is enabled (no shutdown), because the wide area network port and LAN port are disabled by default during factory settings. You can use the "load network" or "config network" command to read the configuration file on the TFTP server. Note that both methods only read the original backup configuration into the vro memory and do not actually modify NVRAM. Therefore, you need to use the preceding command to save the configuration in the memory to NVRAM. The flexible use of NVRAM recovery can also bring a lot of convenience to daily maintenance. For example, if you want to configure multiple vrouters in a similar way, you can configure a vro first, back up the configuration file to the TFTP server, and use it as a template, the configuration file of other routers is changed with a slight modification. You can quickly configure multiple routers by using the recovery method. During system upgrade and expansion, You need to replace the original router with a vro with higher performance, and the original configuration does not need to be changed. Using this "clone" method can achieve half the performance.