Cloudflare Apple Armidale Consulting Active use and maintenance of network protocols is an important way to ensure that protocols remain interoperable and extensible over time. Techniques such as intentionally exercising extension points with non-meaningful values (referred to as "grease") or adding variability to how protocol elements are used help generate this active use. Grease and variability are used across various protocols developed by the IETF. This document discusses considerations when designing and deploying grease and variability mechanisms, and provides advice for making them as effective as possible.