Overwrite running configuration instead of merging on a Cisco router

To replace the current running configuration with a saved Cisco IOS configuration file, use the configure replace command in privileged EXEC mode.

Router#configure replace flash:test.cfg

This command will replace (NOTE: not merge) the running configuration with the configuration in the test.cfg file. This command was introduced in 12.3(7)T

here’s a example of the effect:

Router#ship ip int short

Is the IP address of the interface ok? Method Status Protocol

FastEthernet0/0 10.10.10.3 YES manual up up

FastEthernet0/1 10.1.1.1 YES manual up up

Serial0/3/0 unassigned YES not administratively configured down down

Router#configure replace flash:test.cfg

This will apply all necessary additions and deletions.

to replace the current running configuration with the

contents of the specified configuration file, which is

it’s supposed to be a complete setup, not a partial one

setting. Enter Y if you are sure you want to continue. ? [no]: there

Total number of passes: 1

Revert Done

r1#

Dec 18 00:44:05.927: Rollback: Lock acquired configuration.

Dec 18 00:44:07.703: %PARSER-3-CONFIGNOTLOCKED: Unlock requested by process ‘3’.

Configuration not locked.

Dec 18 00:44:08.819: %LINK-5-CHANGED: Interface FastEthernet0/1, changed state to administratively down

r1#ship ip int short

Is the IP address of the interface ok? Method Status Protocol

FastEthernet0/0 10.10.10.3 YES manual up up

FastEthernet0/1 10.1.1.1 YES manual administratively down down

Serial0/3/0 unassigned YES not administratively configured down down

Consider the following:

1) The name of the router has changed

2) FastEthernet 0/1 no longer has an IP address

3) FastEthernet 0/1 is down

This is great since instead of just MERGE a configuration, the command REPLACES the configuration. You can override the running configuration from many places:

r1#configure replace?

file: URL of the configuration file that will replace the running configuration

cns: URL of the configuration file that will replace the running configuration

flash: URL of the configuration file that will replace the running configuration

ftp: URL of the configuration file that will replace the running configuration

http: URL of the configuration file that will replace the running configuration

https: URL of the configuration file that will replace the running configuration

null: URL of the configuration file that will replace the running configuration

nvram: URL of the configuration file that will replace the running configuration

pram: URL of the configuration file that will replace running-config

rcp: URL of the configuration file that will replace the running configuration

scp: URL of the configuration file that will replace the running configuration

system: URL of the configuration file that will replace the running configuration

tftp: URL of the configuration file that will replace the running configuration

xmodem: URL of the configuration file that will replace the running configuration

ymodem: URL of the configuration file that will replace the running configuration

So you could have a backup configuration in flash or on a TFTP server and immediately restore it to the running configuration.