CCNA RnS #15: Memory Types



CCNA RnS #15 – Types of Memory

In this article let’s talk about various types of memory that exist in Cisco devices and their purpose. Cisco devices use the configuration file that is used to determine the current feature functioning of the device. When you configure a device, the commands you enter go to the Random-access Memory (RAM). This configuration is called the running configuration. When a device gets a reboot or power cycle, this RAM lost its data. This is the reason it is always a best practice to write the configuration to the permanent storage.

Cisco devices have the following storage/memories –

Random-access Memory – also known as DRAM. It is a working storage of the device where temporary data or active configuration is saved – such as running-configuration, ARP table, Routing Table etc.

Flash Memory – stores the fully functional Cisco Operating System file (Cisco IOS image). This is the location where the router finds its operating system when booting up. This flash memory can also be used to store backup files, licenses, and other configuration files. You can consider the same as a removable memory card or a chip inside the router.

Read Only Memory (ROM) – stores the boot helper image that is loaded when the switch is first power on. This bootstrap program identifies the working IOS image from the flash and manages to load the files in RAM.

NVRAM – Non-volatile RAM stores the initial configuration or start-up configuration file that is used when the switch is first powered on and when the switch is reloaded. The startup configuration file is the version of the running configuration file. It is updated when you save the configuration using the write memory or wr command.

Managing the memories

Managing memories include the tasks such as copying, and deleting various types. For example, when you change the device configuration, this change is stored in the RAM and change the device function immediately. However, when the router is reloaded, this change is lost and the old configuration is restored.

Router# config
Router(config)#hostname CiscoRTR

<Router gets reloaded>

As the changes were not saved, router restored to the old configuration with below hostname


Now user needs to re-enter the changes and save the configuration so that it is not lost after the device reload or power failure.

Router# config
Router(config)#hostname CiscoRTR
CiscoRTR# wr

The “wr” command is short for “write memory”. It means whatever changes that are made to RAM should go to the startup configuration file that is stored in NVRAM. You can also use the below command to perform the same operation (saving running configuration to startup configuration)

CiscoRTR# copy running-config startup-config
Syntax – copy <Source file> <Destination file>

With the above command changes are saved permanently. However, there are scenarios where you need to erase the switch configuration completely like – sending the device to another location or another environment where the configuration will be completely new.

write erase
erase startup-config
erase nvram

All three command does the same thing – erase the startup configuration. A device without startup configuration boots with an empty start-up configuration.

There is no command to erase the content of the running configuration – it can only be erased if the device is power cycled. I hope you find this informative!

 Continue Reading...

No comments