Router Configuration Management

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By Ivan Pepelnjak

Cisco IOS releases 12.3(14)T and 12.4 include fundamental router configuration management tools that the network engineers have been sorely missing for the last 20 years. The configuration management tools include the following features:

Contents

If you need professional help in planning, developing or deploying router configuration management tools in your network, contact the author or NIL's Professional Services team

Configuration change notification and logging

The Configuration Change Notification feature allows you to monitor changes to router configuration without deploying AAA exec command authentication and accounting (only available with TACACS+ servers). After you configure it, all the configuration commands entered on the router are stored in a circular buffer (you can even specify its length) and optionally sent to a syslog server.

Read more in the Router Configuration Management IP corner article ...

Contextual configuration difference

If you don’t log the router configuration commands on an external syslog server, one of the first questions you’d ask when being presented with a malfunctioning router would be “What were the recent configuration changes on this box?” The Contextual Configuration Difference feature is supposed to answer this question as long as you have a copy of a complete working configuration file. Startup configuration is usually a good starting point or you could use the Router Configuration Archive feature to generate snapshots of the router configuration.

The Contextual Configuration Difference feature is not perfect; there are a few IOS configuration constructs (for example, policy maps) which it cannot process properly.

Read more in the Router Configuration Management IP corner article ...

Router configuration archive

Router configuration archive functionality was introduced in IOS releases 12.3T and 12.4. It is a simple, yet powerful concept: every time the router operator requests it (or periodically, if so configured), the router stores its current configuration on an external storage. The external file names can include router name, configuration date-and-time, as well as a configuration version number.

Due to the tight integration with the IOS file system, you can store archived configurations using any file transfer protocol your IOS release supports (FTP, RCP, TFTP, HTTP, HTTPS or SCP), or on Class C flash systems, internal drives, or USB drives.

Read more in the Keep Track of Router Configurations with Configuration Archive article ...

Configuration rollback

The Configuration Rollback feature allows you to replace a running configuration with another configuration previously taken from the same router; an operation that would usually require a router reload. It uses the Contextual configuration difference feature to identify changes between the router configurations and applies to changes trying to bring the running configuration as close to the desired one as possible.

As the Contextual configuration difference is not perfect, the Configuration rollback feature performs several retries and reports the trouble spots if it fails to synchronize the configurations in five retries.

Read more in the Replacing Configuration on a Working Router IP corner article ...


Configuration replace

The Configuration rollback feature can be used to replace the running configuration with any configuration of your choice, but it lacks an important safeguard: if the new configuration breaks your connectivity with the router, there’s no way to revert back to the working configuration.

The Configuration replace feature adds the needed safety measures: it archives the current configuration, uses the Configuration rollback feature to replace it with the target configuration and tries to revert back to the archived configuration if the change is not confirmed within the specified time interval.

Read more in the Replacing Configuration on a Working Router IP corner article

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