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Optimizing SDN Updates With Transient Consistency Guarantees
Citation key F-OSDNU-15
Author Foucard, Damien
Year 2015
Address Berlin, Germany
Month March
School Technische Universität Berlin
Abstract Software-defined networking (SDN) is a paradigm rich of opportunities. The administrator defines a simple global policy in the control plane and the controller automatically translates it into routing tables of each switch, thus shielding the administrator from the complexity of vendor-specific switch configurations. Hence, the administrator simply needs to request the controller to enforce a particular constraint, and it will automatically compute a new policy in keeping with this constraint, and updates the network to enforce this policy. Unfortunately, while each singular policy is consistent with specified constraints, the network can remain for an arbitrary large amount of time in a transient state violating them if no specific measure is taken. To avoid this problem, the controller should make sure that the network can only go through transient states conforming to specified constraints, which requires scheduling some updates before others. However, this possibly implies that many switches must wait for others to implement the new policy. A shortest possible update schedule – reducing the latency before the new policy is enforced to the minimum while respecting specified constraints– appears then desirable but computing it induces a high computational cost, potentially not affordable in real time. We consider two constraints: loop-freedom (no packet should loop) and waypoint enforcement (all packets must traverse a middlebox). Loop-freedom is desirable because, although packets caught in loops are usually automatically removed (e.g., with TTL), they represent an undesirable load. Waypoint enforcement is a key feature for Network Function Virtualization and is of particular relevance in security-critical environment, where allowing packets to bypass a middlebox even for a short time already represents an unacceptable risk. An ideal algorithm for computing an update schedule would be easy to compute (minimized computational cost), update the network quickly (routers implementing new policy in minimal time), and offer strong consistency guarantees (maximized number of constraints ensured). Unfortunately, as we show in this work, it appears that this Graal does not exist, and favoring one dimension comes at the expense of another. Hence, balances need to be struck. Accordingly, we consider a variety of settings, favoring in turn one dimension or the other, and in each case present optimized algorithms and highlight caveats. In addition, we implement a framework in which we simulate our algorithms and measure their performance, and present our results, the framework’s modular design allowing for an easy expansion.
Bibtex Type of Publication Master Thesis
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