If all steps were followed in Labs 1 and 2, the switch, labsw1, has two copies of the configuration: the running configuration (running-config) and the startup configuration stored on the switch (startup-config). The startup configuration is stored on the switch even with the switch is powered down. The running configuration only exists when the switch is powered on, and the startup-config is loaded into RAM. These two configurations are stored in different memory on the switch.
Types of Memory
Cisco devices have four types of memory:
• ROM
• Flash memory
• NVRAM - Non-volatile RAM
• RAM, sometimes called DRAM (Dynamic Random Access Memory)
ROM is the least exciting and holds very important low level processes. One such process is the POST process used at bootup: Power On Self Test.
Flash memory holds a copy of the IOS. It is not affected by a loss of power, wihch insures that a copy of IOS is available at bootup.
NVRAM, Non-volatile RAM, stores the startup configuration. It is not affected by power loss, which insures that a copy of the startup configuration is available at bootup.
RAM memory is where all of the work of switching and routing take place. The IOS loads into RAM, then the startup configuration, and finally, the device begins to do its work. All information held in RAM is lost when power is lost or the device is reloaded.
Understanding how memory is used during the boot process may also be on the exam. The (simple) boot process for routers and switches:
- Power-on self-test (POST)
- Read IOS into RAM from Flash memory
- Read startup-config into DRAM from NVRAM
At this point, the device has a running configuration.
Cisco emphasizes that there are two configurations in the router or switch. The two configurations are the startup-config and the running-config. Normally, the data in these two file should be the same; however, it is important to remember that commands entered in configuration mode (configure terminal) are made to the running-config, not to the startup-config. If changes are made, but not saved, the running-config and the startup-config are not the same, and the changes will not available when the switch or router or switch is rebooted.
Changes made to the running-config are saved to the startup-config by the command "copy running-config startup-config". This command copies the running configuration from DRAM to NVRAM. The saved configuration will be used at the next reboot.
