difference between running-config and startup-config

[pdenableetoavit19698]

hi all,

any of you that can clarify the difference between this two? when to use/edit one or the other?

If want to update a Switch with an uptodate configuration which one should I update it with, the running one or the startup?

Thank you!

[Martin L]

Basically difference between running-config and startup-config is any change or changes u make since bootup. Switch boots, loads saved startup cofig from switch flash storage drive and runs on startup config. These two are the same at the moment if u didn't make any changes.  Anything u add, change or edit to startup config will be your running config. Your startup config becomes "old config".   If u save running config, it will be come startup config next time u reboot switch. If u don't save any changes and reboot, switch goes back to startup config. 

Another significant difference is start-up config is stored "permanently" on flash or usb of tftp server as a text file that u can read, edit with text editor.  Running-config is stored in RAM memory and is not permanent unless u save it.

Regards, ML
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[pdenableetoavit19698]

thanks @Martin L 

so the best way to "update" a switch with a newer config is to copy the config file of the startup config from a usb to the startup config of the SW? correct?

is it then saved automatically for next reboot or need to do another command for that?

thanks !

[Martin L]

I was in process of editing my 1st post when u replied.  To clarify, Running-config is loaded and stored in switch memory; it is not permanent and could be lost (if u reboot before saving it or switch crashes).  Start-up config is stored "permanently" on switch memory chip or flash.

Yes, You can copy startup config from usb to switch flash and reboot switch (or boot switch).  You can edit current start up file with text editor; you can copy any other config file to switch and renamed it to start-up config in order for switch to loaded.

However, I would say the best way to "update" a switch is to run switch (boot it up), then make changes, and save those changes with write command or copy running-config start-up config command (copy run start in short)  it as startup config. You can also boot switch up and copy any configurations from notepad to your CLI console.  You can also use Putty to send saved config file to any running switch and save it at the end. 

Regards, ML
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[M02@rt37 · Accepted solution]

Hello @pdenableetoavit19698 ,

In networking, the terms "running configuration" and "startup configuration" refer to two different configuration files on a network device, such as a switch or router. These files serve distinct purposes, and understanding the difference between them is essential for network management and maintenance.*

Running Configuration: The running configuration, also known as the "current configuration" or "active configuration," is the configuration that is currently active and operational on the network device. It reflects the device's current settings and how it's functioning in real-time. You typically view and edit the running configuration when you want to make temporary changes to the device's settings. Changes made to the running configuration take effect immediately and impact the device's operation as soon as they are applied using commands like 'configure terminal' or by using a configuration management tool. These changes are not saved across device reboots.

Startup Configuration: The startup configuration, also known as the "saved configuration" or "boot configuration," is the configuration that is saved on the device's non-volatile memory (often referred to as NVRAM or similar). It represents the configuration that will be loaded and applied to the device when it boots up or is restarted. It serves as the device's baseline configuration. You typically view and edit the startup configuration when you want to make permanent changes to the device's settings. Changes made to the startup configuration are saved across reboots, ensuring that the device maintains the desired configuration even after power cycles or unexpected reboots.

-- If you want to apply configuration changes immediately and temporarily (for example, to troubleshoot or test a new configuration), edit the running configuration.

-- If you want to ensure that the switch retains the desired configuration across reboots and that it always starts with a specific configuration, edit the startup configuration.

In practice, netadmin often make changes to the running configuration first, test them to ensure they work as expected, and then save those changes to the startup configuration if they want them to persist. 

To copy the running configuration to the startup configuration (making your temporary changes permanent), you can use commands like 'write memory'' 'copy running-config stratur-config', or 'copy run start' depending on the network device's command-line interface.

[Joseph W. Doherty]

Just to add a point to what the others have already described, although you can copy to/from either the startup or running config "files", the startup config file is an actual file of configuration statements stored on flash and is replaced (i.e. totally over written) if you copy a file to it.  The running config "file" isn't permanently stored and is not replaced when you copy to it, instead the file being copied to it (assuming its configuration statements) is merged with the whatever is currently active.

The startup config file, isn't (to my knowledge) generally editable, although you can copy it external to the device, edit on the external device and then copy back to it (replacing it).

The running config is "edited" when you enter "configuration terminal" mode or you copy configuration statements into it.

BTW, some Cisco device OSs (XR and NX) now support a two stage running configuration commit.

[Richard Burts]

To expand on the explanation by Joseph we tend to think of running config and startup config as files. That is true of startup config but not true of running config. Running config is a dynamic data structure created at boot up by the device. Running config is initialized using the content of startup config (and if startup config does not exist then running config is initialized by the configuration dialogue). Running config is modified by using config terminal or by copying commands to it. If the device is rebooted or powered down the content of running config disappears and a new running config is created when the device completes it boot process.

Joseph makes a good point about what happens if you copy commands to startup config or to running config. As a file when you copy something to startup it is a complete replacement of the existing file by a new file. But if you copy something to running config it a merge operation.

[Joseph W. Doherty]

Reading Rick's reply, how a running config is initially built at startup, reminds me the IOS defaults to many, many settings during startup.  Whether it's a config dialogue or a startup config file both just merge modify the IOS defaults.

[Gopinath_Pigili]

Startup configuration means which is already saved configuration...that is stored in NVRAM

Running configuration means current /present configuration that is running one the Switch/router...that is stored in RAM

Both configurations can be used for back up and restore by using FTP/TFTP applications...

If you want to update a Switch with an uptodate configuration...you should use running configuration....

For example, i took weekly backup of startup configuration  on Saturday.....on Monday I did some changes....I took daily backup of running configuration...on Tuesday...assume that your switch configuration accidentally been deleted...if you want to restore the switch with uptodate...including the changes you did on Monday...You should restore the running configuration.....

I hope the above information is useful...

Thanks