Regular Expressions for Network Engineers


How many times were you working on a task which involved either updating all instances of a piece of configuration or creating a new configuration piece at multiple points on a network device?  You have translated the requirements into functional syntax, a blueprint, for the specific hardware platform, now it’s time to implement it 10’s of times on the device. How do you implement it on the device?

For small and non-routine one-off tasks, the quickest way may be to jump on the device and repeat the manual labor N times at different places and with slight variations, where N is hopefully a relatively small number worth this manual approach. This may also be true for a junior network engineer who may not know other efficient methods of achieving it.

This is a type of automation as we aim to reduce if not eliminate manual processes that are very well defined and certainly repeatable. While automation can go a long way where we can have multiple devices or device groups, automated login to these, implementation of config and finally verification of status and rollback if needed, all being launched in order by a single orchestrating script – say an Ansible Playbook. Let’s keep that for some other day and talk about simple config generation on a single device that we can manually apply.

Ok, enough of the need for regular expressions (regex), let’s get started.


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