To provide high availability and fault-tolerance, SDN control planes should be distributed. However, distributed control planes are challenging to design and bootstrap, especially if this is done in-band, without a dedicated control network, and without relying on legacy protocols. We present Medieval, a plug & play, distributed control plane that supports automatic topology discovery and management, as well as flexible control plane membership: controllers can be added and removed dynamically. Medieval comes with interesting robustness guarantees and is provably self-stabilizing: from any initial topology, the controllers quickly self-organize and establish a communication channel among themselves. Given the resulting managed control plane, arbitrary network control services can be implemented on top. Interestingly, Medieval is also self-reliant, in the sense that it is based on OpenFlow only, and does not require any legacy protocol to bootstrap.

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