Safe, Efficient, and Robust SDN Updates by Combining Rule Replacements and Additions

IEEE Disruption-free updates are a key primitive to effectively operate SDN networks and maximize the benefits of their programmability. In this paper, we study how to implement this primitive safely (with respect to forwarding correctness and policies), efficiently (in terms of consumed network resources) and robustly to unpredictable factors, such as delayed message delivery and processing. First, we analyze the fundamental limitations of prior proposals, which either: 1) progressively replace initial flow rules with new ones or 2) instruct switches to maintain both initial and final rules. Second, we show that safe, efficient, and robust updates can be achieved by leveraging a more general approach. We indeed unveil a dualism between rule replacements and additions that opens new degrees of freedom for supporting SDN updates. Third, we demonstrate how to build upon this dualism. We propose FLIP, an algorithm that computes operational sequences combining the efficiency of rule replacements with the applicability of rule additions. FLIP identifies constraints on rule replacements and additions that independently prevent safety violations from occurring during the update. Then, it explores the solution space by swapping constraints that prevent the same safety violations, until it reaches a satisfiable set of constraints. Fourth, we perform extensive simulations, showing that FLIP can significantly outperform prior work. In the average case, it guarantees a much higher success rate than algorithms only based on rule replacements, and massively reduces the memory overhead needed by techniques solely using rule additions

Continuous Network Update With Consistency Guaranteed in Software-Defined Networks

Network update enables Software-Defined Networks (SDNs) to optimize the data plane performance. The single update focuses on processing one update event at a time, i.e., updating a set of flows from their initial routes to target routes, but it fails to handle continuously arriving update events in time incurred by high-frequency network changes. On the contrary, the continuous update proposed in ``Update Algebra'' can handle multiple update events concurrently and respond to the network condition changes at all times. However, ``Update Algebra'' only guarantees the blackhole-free and loop-free update. The congestion-free property cannot be respected. In this paper, we propose Coeus to achieve the continuous update while maintaining consistency, i.e., ensuring the blackhole-free, loop-free, and congestion-free properties simultaneously. Firstly, we establish the continuous update model based on the update operations in update events. With the update model, we dynamically reconstruct the operation dependency graph (ODG) to capture the relationship between update operations and link utilization variations. Then, we develop a composition algorithm to eliminate redundant operations in update events. To further speed up the update procedure, we present a partition algorithm to split the operation nodes of the ODG into a series of suboperation nodes that can be executed independently. The partition algorithm is proven to be optimal. Finally, extensive evaluations show that Coeus can improve the update speed by at least 179% and reduce redundant operations by at least 52% compared with state-of-the-art approaches when the arrival rate of update events equals three times per second. IEE