The difference between Run and Start and how to save!

In this post I am going to explain the difference between the running and startup configuration files that are stored on Cisco devices.

I will show you how to view both of these configuration files and how to save changes from the running to the startup configuration file (or vice versa).

Let's dive in!

Running-config vs Startup-config

Before we start looking at commands, let me explain the difference between these two important configuration files:

Running Configuration (running-config): This is the configuration that is currently active and running in the device's RAM. Any changes you make to the device configuration are immediately applied to the running-config. However, this configuration is volatile - if the device loses power or is restarted, all changes in the running-config will be lost unless they have been saved to the startup-config.

Startup Configuration (startup-config): This is the configuration file that is stored in the device's non-volatile memory (NVRAM). When the device boots up, it loads this configuration file. This file persists through reboots and power cycles.

Viewing the Configuration Files

To view the running configuration, use the following command:

Router# show running-config

To view the startup configuration, use:

Router# show startup-config

You can also use the abbreviated versions:

Router# show run
Router# show start

Saving Your Configuration

When you make changes to your device configuration, those changes are applied to the running-config. To make these changes permanent (so they survive a reboot), you need to save them to the startup-config.

There are several ways to save your configuration:

Method 1: Copy Running to Startup

Router# copy running-config startup-config

Or the abbreviated version:

Router# copy run start

Method 2: Write Memory

Router# write memory

Or even shorter:

Router# wr

Method 3: Write

Router# write

All of these methods accomplish the same thing - they copy the running configuration to the startup configuration.

Video Demonstration

Watch this video to see these concepts in action:

Important Notes

Here are some key points to remember:

• Changes made in configuration mode are immediately applied to the running-config
• The running-config is stored in RAM and will be lost if the device restarts without saving
• The startup-config is stored in NVRAM and persists through reboots
• Always save your configuration after making changes if you want them to be permanent
• You can compare the two configurations to see what changes haven't been saved yet

Copying Startup to Running

Sometimes you might want to reload the startup configuration without rebooting the device. You can copy the startup-config to the running-config:

Router# copy startup-config running-config

This will merge the startup configuration with the current running configuration. Be careful with this command as it can cause unexpected behavior.

Conclusion

Understanding the difference between running-config and startup-config is fundamental to working with Cisco devices. Remember:

• Running-config = current active configuration in RAM (volatile)
• Startup-config = saved configuration in NVRAM (non-volatile)
• Always save your changes with copy run start or write memory

This knowledge will serve you well as you continue your CCNA studies and work with Cisco networking equipment.