It seems to me that a fundamental problem with referencing Open Source software is that in much (not all) of the Open Source world, rapid innovation and evolution is valued more than stable protocol interfaces. There is a tendency to rely on users to frequently update their software, which is seen as giving developers freedom to change interfaces on relatively short notice. Of course that's an oversimplification. In practice good open source developers are careful to avoid abrupt changes to interfaces; instead they create new interfaces and deprecate old ones. But since one of the oft-touted benefits of Open Source is to allow software systems to evolve rapidly, this sometimes also results in new protocol features being deployed rapidly to the point that it impairs interoperability between new and old implementations. This causes a great many problems other than just protocol interoperability failures, including dependency hell. So part of the effort to improve cooperation between IETF and Open Source developers - who tend to have similar motivations even if their methods differ - might be in convincing them that they would benefit from more stable interfaces - at least on the wire - or at least encouraging them to define protocols so that they are cleanly extensible, and defining a baseline for interoperability even as they extend protocols to accommodate new features. And actually it might be the case that IETF could learn something about protocol extensibility from people who have struggled to accommodate rapid evolution of their software. Keith