Software-defined network (SDN) architectures raise the question of how to deal with situations where the indirection via the control plane is not fast enough or not possible. In order to provide a high availability, connectivity, and robustness, dependable SDNs must support basic functionality also in the data plane. In particular, SDNs should implement functionality for inband network traversals, e.g., to find failover paths in the presence link failures. This paper shows that robust inband network traversal schemes for dependable SDNs are feasible, and presents three fundamentally different mechanisms: simple stateless mechanisms, efficient mechanisms based on packet tagging, and mechanisms based on dynamic state at the switches. We show how these mechanisms can be implemented in today’s SDNs and discuss different applications.

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