This paper addresses one serious SDN-specific attack, i.e., data-to-control plane saturation attack, which overloads the infrastructure of SDN networks. In this attack, an attacker can produce a large amount of table-miss packet_in messages to consume resources in both control plane and data plane. To mitigate this security threat, we introduce an efficient, lightweight and protocol-independent defense framework for SDN networks. Our solution, called FloodGuard, contains two new techniques/modules: proactive flow rule analyzer and packet migration. To preserve network policy enforcement, proactive flow rule analyzer dynamically derives proactive flow rules by reasoning the runtime logic of the SDN/OpenFlow controller and its applications. To protect the controller from being overloaded, packet migration temporarily caches the flooding packets and submits them to the OpenFlow controller using rate limit and round-robin scheduling. We evaluate FloodGuard through a prototype implementation tested in both software and hardware environments. The results show that FloodGuard is effective with adding only minor overhead into the entire SDN/OpenFlow infrastructure.

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FloodGuard: A DoS Attack Prevention Extension in Software-Defined Networks

Having gained momentum from its promise of centralized control over distributed network architectures at bargain costs, software-defined Networking (SDN) is an ever-increasing topic of research. SDN offers a simplified means to dynamically control multiple simple switches via a single controller program, which contrasts with current network infrastructures where individual network operators manage network devices individually. Already, SDN has realized some extraordinary use cases outside of academia with companies, such as Google, AT&T, Microsoft, and many others. However, SDN still presents many research and operational challenges for government, industry, and campus networks. Because of these challenges, many SDN solutions have developed in an ad hoc manner that are not easily adopted by other organizations. Hence, this paper seeks to identify some of the many challenges where new and current researchers can still contribute to the advancement of SDN and further hasten its broadening adoption by network operators.

Advancing Software-Defined Networks: A Survey

We present Minesweeper, a tool to verify that a network satisfies a wide range of intended properties such as reachability or isolation among nodes, waypointing, black holes, bounded path length, load-balancing, functional equivalence of two routers, and fault-tolerance. Minesweeper translates network configuration files into a logical formula that captures the stable states to which the network forwarding will converge as a result of interactions between routing protocols such as OSPF, BGP and static routes. It then combines the formula with constraints that describe the intended property. If the combined formula is satisfiable, there exists a stable state of the network in which the property does not hold. Otherwise, no stable state (if any) violates the property. We used Minesweeper to check four properties of 152 real networks from a large cloud provider. We found 120 violations, some of which are potentially serious security vulnerabilities. We also evaluated Minesweeper on synthetic benchmarks, and found that it can verify rich properties for networks with hundreds of routers in under five minutes. This performance is due to a suite of model-slicing and hoisting optimizations that we developed, which reduce runtime by over 460x for large networks.

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A General Approach to Network Configuration Verification

Software-defined networking (SDN) offers greater flexibility than traditional distributed architectures, at the risk of the controller being a single point-of-failure. Unfortunately, existing fault-tolerance techniques, such as replicated state machine, are insufficient to ensure correct network behavior under controller failures. The challenge is that, in addition to the application state of the controllers, the switches maintain hard state that must be handled consistently. Thus, it is necessary to incorporate switch state into the system model to correctly offer a "logically centralized" controller.We introduce Ravana, a fault-tolerant SDN controller platform that processes the control messages transactionally and exactly once (at both the controllers and the switches). Ravana maintains these guarantees in the face of both controller and switch crashes. The key insight in Ravana is that replicated state machines can be extended with lightweight switch-side mechanisms to guarantee correctness, without involving the switches in an elaborate consensus protocol. Our prototype implementation of Ravana enables unmodified controller applications to execute in a fault-tolerant fashion. Experiments show that Ravana achieves high throughput with reasonable overhead, compared to a single controller, with a failover time under 100ms.

Ravana: controller fault-tolerance in software-defined networking

NetKAT is a domain-specific language and logic for specifying and verifying network packet-processing functions. It consists of Kleene algebra with tests (KAT) augmented with primitives for testing and modifying packet headers and encoding network topologies. Previous work developed the design of the language and its standard semantics, proved the soundness and completeness of the logic, defined a PSPACE algorithm for deciding equivalence, and presented several practical applications. This paper develops the coalgebraic theory of NetKAT, including a specialized version of the Brzozowski derivative, and presents a new efficient algorithm for deciding the equational theory using bisimulation. The coalgebraic structure admits an efficient sparse representation that results in a significant reduction in the size of the state space. We discuss the details of our implementation and optimizations that exploit NetKAT's equational axioms and coalgebraic structure to yield significantly improved performance. We present results from experiments demonstrating that our tool is competitive with state-of-the-art tools on several benchmarks including all-pairs connectivity, loop-freedom, and translation validation.

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A Coalgebraic Decision Procedure for NetKAT

Software bugs are inevitable in software-defined networking control software, and troubleshooting is a tedious, time-consuming task. In this paper we discuss how to improve control software troubleshooting by presenting a technique for automatically identifying a minimal sequence of inputs responsible for triggering a given bug, without making assumptions about the language or instrumentation of the software under test. We apply our technique to five open source SDN control platforms---Floodlight, NOX, POX, Pyretic, ONOS---and illustrate how the minimal causal sequences our system found aided the troubleshooting process.

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Troubleshooting blackbox SDN control software with minimal causal sequences

Network operators often need to adapt the configuration of a network in order to comply with changing routing policies. Evolving existing configurations, however, is a complex task as local changes can have unforeseen global effects. Not surprisingly, this often leads to mistakes that result in network downtimes. We present NetComplete, a system that assists operators in modifying existing network-wide configurations to comply with new routing policies. NetComplete takes as input configurations with “holes” that identify the parameters to be completed and “autocompletes” these with concrete values. The use of a partial configuration addresses two important challenges inherent to existing synthesis solutions: (i) it allows the operators to precisely control how configurations should be changed; and (ii) it allows the synthesizer to leverage the existing configurations to gain performance. To scale, NetComplete relies on powerful techniques such as counter-example guided inductive synthesis (for link-state protocols) and partial evaluation (for path-vector protocols). We implemented NetComplete and showed that it can autocomplete configurations using static routes, OSPF, and BGP. Our implementation also scales to realistic networks and complex routing policies. Among others, it is able to synthesize configurations for networks with up to 200 routers within few minutes.

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NetComplete: Practical Network Wide Configuration Synthesis with Autocompletion

Computer networks are hard to manage. Given a set of high-level requirements (e.g., reachability, security), operators have to manually figure out the individual configuration of potentially hundreds of devices running complex distributed protocols so that they, collectively, compute a compatible forwarding state. Not surprisingly, operators often make mistakes which lead to downtimes. To address this problem, we present a novel synthesis approach that automatically computes correct network configurations that comply with the operator's requirements. We capture the behavior of existing routers along with the distributed protocols they run in stratified Datalog. Our key insight is to reduce the problem of finding correct input configurations to the task of synthesizing inputs for a stratified Datalog program. To solve this synthesis task, we introduce a new algorithm that synthesizes inputs for stratified Datalog programs. This algorithm is applicable beyond the domain of networks. We leverage our synthesis algorithm to construct the first network-wide configuration synthesis system, called SyNET, that support multiple interacting routing protocols (OSPF and BGP) and static routes. We show that our system is practical and can infer correct input configurations, in a reasonable amount time, for networks of realistic size (> 50 routers) that forward packets for multiple traffic classes.

Network-wide Configuration Synthesis

Concurrency violations are an important source of bugs in Software-Defined Networks (SDN), often leading to policy or invariant violations. Unfortunately, concurrency violations are also notoriously difficult to avoid, detect and debug. This paper presents a novel approach and a tool, SDNRacer, for detecting concurrency violations of SDNs. Our approach is enabled by three key ingredients: (i) a precise happens- before model for SDNs that captures when events can happen concurrently; (ii) a set of sound, domain-specific filters that reduce reported violations by orders of magnitude, and; (iii) a sound and complete dynamic analyzer, based on the above, that can ensure the network is free of harmful errors such as data races and per-packet incoherence. We evaluated SDNRacer on several real-world OpenFlow controllers, running both reactive and proactive applications in large networks. We show that SDNRacer is practically effective: it quickly pinpoints harmful concurrency violations without overwhelming the user with false positives.

SDNRacer: concurrency analysis for software-defined networks

Computer networks are hard to manage. Given a set of high-level requirements (e.g., reachability, security), operators have to manually figure out the individual configuration of potentially hundreds of devices running complex distributed protocols so that they, collectively, compute a compatible forwarding state. Not surprisingly, operators often make mistakes which lead to downtimes.

Ahmed El-Hassany

Papers

Troubleshooting blackbox SDN control software with minimal causal sequences

NetComplete: Practical Network Wide Configuration Synthesis with Autocompletion

Network-wide Configuration Synthesis

SDNRacer: concurrency analysis for software-defined networks

Network-Wide Configuration Synthesis