Identify Changes in Router Configurations

Articles » Identify Changes in Router Configurations

If you’ve ever had to manage and configure more than a few routers in a production environment, there probably was a moment when you had to figure out what changes were made to a device configuration.

Answering that question seems to be an easy task; after all, device configurations are just text files:

• Periodically collect device configurations and store them somewhere (shared disk, database, or source code repository like Git)
• Whenever you have to figure out what changed, run a utility like diff to identify changes in text files.

Several vendors took this approach when implementing network operating systems on top of Linux (for example, Cisco Nexus OS or Arista EOS). Unfortunately, the differences in text files sometimes fail to identify the gist of the changes made to more complex device configurations.

Cisco decided to do something better. Their Contextual Configuration Diff utility (introduced in Cisco IOS release 12.4) generates a set of configuration commands that must be removed or added to the starting configuration to reach the target configuration.