Startup-running config

[SathishkumarSaravanan0348]

Hi Experts,

When I do certain changes in the CLI and then issued command copy running config startup config 

1. I am understood that the running config are saved to startup config(NVRAM) and when issued sh startup, it is showing.

2. Same I have done some changes and given the command copy startup running config.

eg: int gig0/0/1

description backup LAN

ip add 10.240.25.1 255.255.255.0

no shutdown

The above config is in running and I did not saved (wr).

In startup config I could see the interface gig0/0/1 is in default mode. My assumption is that when I try to copy the startup config to running my interface gig0/0/1 should become default, but it was not happened.

Can u guys explain what is the significant difference when we give copy startup to running config.

Regards,

Sathish

[balaji.bandi]

startup config will be loaded automatically when the device start.

runninng config will be temporarly stored as running, until you issue command wr or copy manually to startup (your understand here is correct)

it will not work or take effective copy from startup to running config ( take effective in the live)

if you want to take effecttive of startup it has to rebooted or you can manually do the same way you on running config.

[SathishkumarSaravanan0348 · Accepted solution]

Thanks Balaji for the answers.

[luis_cordova]

Hi @SathishkumarSaravanan0348 

Check this link:

https://www.velocityreviews.com/threads/copy-startup-config-running-config-why-is-this-command-not-used.495513/

Regards

[SathishkumarSaravanan0348]

Thanks for the link

[Richard Burts]

While they look very similar the commands copy run start and copy start run operate very differently. copy run start results in a complete replacement of the previous startup config file with a new file reflecting the running config. But copy start run is more of an overlay process. Any line found in the startup config will replace the corresponding line of the running config. But any line in the running config for which there is not a corresponding line in startup will continue to be in the config. For example we might have and interface in running config that has this

interface FastEthernet 1

ip address 10.10.10.1 255.255.255.0

ip access-group 101 in

and startup config might have this

interface FastEthernet 1

ip address 20.20.20.2 255.255.255.0

If we copy start run the result will be 

Interface FastEthernet 1 

ip address 20.20.20.2 255.255.255.0

ip access-group 101 in

The reason for the difference in behavior is based on differences between running config and startup config. While startup config is essentially a text file in nvram the running config is a data structure in ram. copy run start interrogates the data structure, takes its content, builds a new text file and that new file replaces the existing startup config. copy start run takes the existing startup config file and feeds it into the syntax processor which updates the existing data structure (does not create a new data structure).

HTH

Rick