Current network routing protocol design is faced with novel challenges due to evolving network scale, various network service demands, and dynamic network states. However, the conventional finite state machine models lack both scalability and flexibility for the description of network routing protocol states. In this article, we enable scalability and flexibility into network routing protocol by exploring and exploiting behavior trees, where behavior trees can reformulate the network routing protocol by characterizing state transformation as action nodes. We first present a generic routing protocol architecture with a comparative analysis of the behavior tree, finite state machine, etc. Then, we propose an implementable functional scheme, which provides a foundation for extending the functionality and enabling flexible configurations towards the network routing protocol. Finally, we design two use cases to verify that behavior trees can effectively replace finite state machines and the excellent scalability of behavior trees in terms of routing protocols.