Generally, in a fresh switch, I see a startup-configuration.

Switch#show startup-config
startup-config is not present

But when I do 'sh run' I see a default running config in it. Where does this default running configuration load from? Is it from the ROM?

When there is no startup-config, then it will not show any startup-config. If I do a 'show run' in a fresh switch it shows me some output (some default settings like the ios version, hostname, interfaces details being set to auto etc). So some details of the running-config are there. Where do these come from?

It can also tried it in a lab.

Do a erase startup-config. Do a reload.

Then do a "sh run". It will show some output. I was just thinking where does this running-config come from?


When IOS boots up, it has an initial state for all settings (i.e. default settings) when it initially loads. The startup configuration is then applied to this initial state. If there is no startup configuration then the initial state of all settings is maintained.

When you do a show run command, IOS displays certain initial state settings (interfaces, etc), plus any modifications to the initial state that were applied to the configuration (either through the startup configuration or through user applied changes). If you want to see the full configuration, including any default settings, you can use show run all instead.


I'm assuming this pertains to Cisco routers/switches. The software itself is going to create a running configuration that contains start and end markers, some default values and an enumeration of the hardware in the box (i.e interfaces).


It comes from the operating system. The IOS creates default values in the running configuration for things like interfaces, etc.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.