Router Memory Details

Posted on January 7, 2011 by milankantony.ml — Leave a comment

Router Memory

Be sure you understand the difference between the following types of router storage.

Memory Type	Characteristics
ROM (read-only memory)	Preprogrammed, non-writable memory containing the bootstrap startup program, an older, smaller-scale version of the operating system (IOS) software, and the Power-on Self-Test (POST) program
Flash	Non-volatile but programmable memory containing the proprietary Cisco operating system (IOS) images
RAM (random access memory)	Volatile memory containing the running operating system and current (unsaved) configuration information
NVRAM (non-volatile RAM)	Non-volatile but persistent memory that contains the backup copy of the startup configuration (startup-config) file and virtual configuration register

The contents of non-volatile memory (such as ROM, flash, and NVRAM) remain when the router is powered off (however, you must modify the configuration registry and NVRAM during password recovery). The contents of volatile memory (RAM) are lost when the router is powered down.

Copy Command List

The router can load a configuration file from:

NVRAM (startup-configuration file by default value 0x2102)
TFTP server

Changes to the configuration are stored in RAM in the running-config file. To save your configuration changes permanently, and to load different versions of the configuration files from various locations, use the copy command in privileged EXEC mode.

Use . . .	To . . .
Router#copy run start	Save the contents of the running-config file to NVRAM
Router#copy start run	Copy the startup-config file into RAM
Router#copy run tftp	Save the contents of the running-config file to a TFTP server
Router#copy start tftp	Save the contents of the startup-config file to a TFTP server
Router#copy tftp start	Copy a configuration file from the TFTP server into NVRAM
Router#copy tftp run	Copy a configuration file from the TFTP server into RAM
Router(config)#tftp-server flash <filename>	Configure a Cisco router as a TFTP server. When using this command, you must specific the location (flash or rom) of the IOS image file as well as the IOS image file name.

You can also use the erase command to delete the configuration files–but be very careful not to erase files you need!

Use . . .	To . . .
Router#erase flash	Delete the contents of Flash memory (deletes the IOS image)
Router#erase start	Erase the contents of the startup-config file
Router#erase nvram	Delete the contents of NVRAM (which also erases startup-config)
Router#reload	Restarts the router

You can also use the following commands to manage system files:

Use . . .	To . . .
show version	Display information about hardware and firmware including the configuration register value
configure memory or copy startup-config running-config	Copy configuration information from another source (like NVRAM)
configure terminal	Configure information into the RAM of a router