It is important to understand what happens when you issue a ‘copy start running’ or ‘copy tftp running’ command. The config stored in the NVRAM (startup-config) or on the TFTP server is ‘read’ into the router line by line and the commands executed. It is not a ‘remove existing config and replace with new’ scenario, but an ‘execute this script over the existing config’ scenario. What this means is that, if you’re messing around and shutdown a number of interfaces or enable a feature that drives the router nuts, simply typing: “copy start running” will not restore the original config. If an interface is in shutdown mode in the running config, and the startup config contains:
!
int eth0
ip address 192.168.0.1
!
the interface will not be ‘unshut’ automatically.
To restore the original configuration from the start-up config you need to reboot the router (unless you have overwritten it already!), or undo the changes manually using the ‘no’ directive.