copy start run
Copy Startup-config Running-config
This command lets you merge your saved config with the running configuration. The command overwrites conflicting infomation such as interface IP addresses but keeps new information in the config.
R1#copy startup-config running-config
In the below example R1's saved configuration is merged with its running configuration.
Now lets merge the configuration, notice that R1's loopback reverted back to 126.96.36.199 while it kept the new loopback1 interface.