A Survey on Efforts to Evolve the Control Plane of Inter-Domain Routing <s> SDN as an Enabling Technology <s> Over the past decade, the complexity of the Internet's routing infrastructure has increased dramatically. This complexity and the problems it causes stem not just from various new demands made of the routing infrastructure, but also from fundamental limitations in the ability of today's distributed infrastructure to scalably cope with new requirements.The limitations in today's routing system arise in large part from the fully distributed path-selection computation that the IP routers in an autonomous system (AS) must perform. To overcome this weakness, interdomain routing should be separated from today's IP routers, which should simply forward packets (for the most part). Instead, a separate Routing Control Platform (RCP) should select routes on behalf of the IP routers in each AS and exchange reachability information with other domains.Our position is that an approach like RCP is a good way of coping with complexity while being responsive to new demands and can lead to a routing system that is substantially easier to manage than today. We present a design overview of RCP based on three architectural principles path computation based on a consistent view of network state, controlled interactions between routing protocol layers, and expressive specification of routing policies and discuss the architectural strengths and weaknesses of our proposal. <s> BIB001 </s> A Survey on Efforts to Evolve the Control Plane of Inter-Domain Routing <s> SDN as an Enabling Technology <s> This article surveys several research challenges in interdomain routing. We introduce and describe these challenges in a comprehensible manner, along with a review of the most compelling contributions and ongoing research efforts addressing each of the exposed issues. During this analysis we identify the relation between these research challenges and now they influence each other. We also present our perspectives on why these issues remain largely unsolved, and point out why some of the proposals made so far have not yet been adopted. We hope this can provide some insight on future directions in this complex research area. <s> BIB002 </s> A Survey on Efforts to Evolve the Control Plane of Inter-Domain Routing <s> SDN as an Enabling Technology <s> In this paper, we review why BGP is a poor candidate to facilitate the next generation of Software Defined Networks (SDN) and propose the Interdomain Management Layer (IML) architecture, a framework for facilitating interdomain resource sharing between these networks. IML uses a concept we call horizontal slicing, that allows SDN networks to become autonomous peers with other ASes, while maintaining centralized, operator-facing policy control and end-to- end flow control across interdomain boundaries. <s> BIB003 </s> A Survey on Efforts to Evolve the Control Plane of Inter-Domain Routing <s> SDN as an Enabling Technology <s> Software Defined Networking (SDN) is an exciting technology that enables innovation in how we design and manage networks. Although this technology seems to have appeared suddenly, SDN is part of a long history of efforts to make computer networks more programmable. In this paper, we trace the intellectual history of programmable networks, including active networks, early efforts to separate the control and data plane, and more recent work on OpenFlow and network operating systems. We highlight key concepts, as well as the technology pushes and application pulls that spurred each innovation. Along the way, we debunk common myths and misconceptions about the technologies and clarify the relationship between SDN and related technologies such as network virtualization. <s> BIB004 </s> A Survey on Efforts to Evolve the Control Plane of Inter-Domain Routing <s> SDN as an Enabling Technology <s> P4 is a high-level language for programming protocol-independent packet processors. P4 works in conjunction with SDN control protocols like OpenFlow. In its current form, OpenFlow explicitly specifies protocol headers on which it operates. This set has grown from 12 to 41 fields in a few years, increasing the complexity of the specification while still not providing the flexibility to add new headers. In this paper we propose P4 as a strawman proposal for how OpenFlow should evolve in the future. We have three goals: (1) Reconfigurability in the field: Programmers should be able to change the way switches process packets once they are deployed. (2) Protocol independence: Switches should not be tied to any specific network protocols. (3) Target independence: Programmers should be able to describe packet-processing functionality independently of the specifics of the underlying hardware. As an example, we describe how to use P4 to configure a switch to add a new hierarchical label. <s> BIB005 </s> A Survey on Efforts to Evolve the Control Plane of Inter-Domain Routing <s> SDN as an Enabling Technology <s> Software Defined Networking envisions smart centralized controllers governing the forwarding behavior of dumb low-cost switches. But are "dumb" switches an actual strategic choice, or (at least to some extent) are they a consequence of the lack of viable alternatives to OpenFlow as programmatic data plane forwarding interface? Indeed, some level of (programmable) control logic in the switches might be beneficial to offload logically centralized controllers (de facto complex distributed systems) from decisions just based on local states (versus network-wide knowledge), which could be handled at wire speed inside the device itself. Also, it would reduce the amount of flow processing tasks currently delegated to specialized middleboxes. The underlying challenge is: can we devise a stateful data plane programming abstraction (versus the stateless OpenFlow match/action table) which still entails high performance and remains consistent with the vendors' preference for closed platforms? We posit that a promising answer revolves around the usage of extended finite state machines, as an extension (super-set) of the OpenFlow match/action abstraction. We concretely turn our proposed abstraction into an actual table-based API, and, perhaps surprisingly, we show how it can be supported by (mostly) reusing core primitives already implemented in OpenFlow devices. <s> BIB006 </s> A Survey on Efforts to Evolve the Control Plane of Inter-Domain Routing <s> SDN as an Enabling Technology <s> The Border Gateway Protocol (BGP) was designed almost three decades ago and has many limitations relating to its fully distributed nature, policy enforcement capabilities, scalability, security and complexity. For example, the control plane can take several minutes to converge after a routing change; this may be unacceptable for real-time network services. Despite many research proposals for incremental improvements and clean-slate redesigns of how inter-domain routing should work, BGP is likely one of the most ossified protocols of the Internet architecture and it has not retrofitted the proposed ideas. In this work, we propose a radical, incrementally deployable Internet routing paradigm in which the control plane of multiple networks is logically centralized. This follows the Software Defined Networking (SDN) paradigm, although at the inter-domain level involving multiple Autonomous Systems (AS). Multi-domain SDN centralization can be realized by outsourcing routing functions to an external contractor, which provides inter-domain routing services facilitated through a multi-AS network controller. The proposed model promises to become a vehicle for evolving BGP and uses the bird's eye view over several networks to benefit aspects of inter-domain routing, such as convergence properties, policy conflict resolution, inter-domain troubleshooting, and collaborative security. In addition to the proposed paradigm, we introduce a publicly available emulation platform built on top of Mininet and the Quagga routing software, for experimenting on hybrid BGP-SDN AS-level networks. As a proof of concept, we focus specifically on exploiting multi-domain centralization to improve BGP's slow convergence. We build and make publicly available a first multi-AS controller tailored to this use case and demonstrate experimentally that SDN centralization helps to linearly reduce BGP convergence times and churn rates with expanding SDN deployments. <s> BIB007 </s> A Survey on Efforts to Evolve the Control Plane of Inter-Domain Routing <s> SDN as an Enabling Technology <s> Given the distributed and business-driven nature of the Internet, economic interests of autonomous systems (ASes) may be incompatible. Previous works studied specific effects of incompatible interests, especially BGP policy conflicts leading to routing and forwarding anomalies. In this paper, we focus on the effects of incompatible interests that do not trigger such anomalies. We take the perspective of a single AS: we show that incompatible interests can have a tangible impact on its business and provide a classification of its unsatisfied interests. Since incompatible interests cannot be solved automatically, our effort is directed to support network managers in their business decisions. Hence, we describe algorithms to identify and assess their impact, as well as a prototype of a warning system aimed at signaling the most relevant unsatisfied interests. We evaluate our prototype on real data from two operational networks. In addition, to illustrate the potential of our system, our evaluation shows that unsatisfied interest are relatively frequent and likely affect a significant amount of traffic in practice. <s> BIB008 </s> A Survey on Efforts to Evolve the Control Plane of Inter-Domain Routing <s> SDN as an Enabling Technology <s> Software-Defined Internet Exchange Points (SDXes) promise to significantly increase the flexibility and function of interdomain traffic delivery on the Internet. Unfortunately, current SDX designs cannot yet achieve the scale required for large Internet exchange points (IXPs), which can host hundreds of participants exchanging traffic for hundreds of thousands of prefixes. Existing platforms are indeed too slow and inefficient to operate at this scale, typically requiring minutes to compile policies and millions of forwarding rules in the data plane. ::: ::: We motivate, design, and implement iSDX, the first SDX architecture that can operate at the scale of the largest IXPs. We show that iSDX reduces both policy compilation time and forwarding table size by two orders of magnitude compared to current state-of-the-art SDX controllers. Our evaluation against a trace from one of the largest IXPs in the world found that iSDX can compile a realistic set of policies for 500 IXP participants in less than three seconds. Our public release of iSDX, complete with tutorials and documentation, is already spurring early adoption in operational networks. <s> BIB009 </s> A Survey on Efforts to Evolve the Control Plane of Inter-Domain Routing <s> SDN as an Enabling Technology <s> The decoupling of control and data plane in software-defined networking (SDN) has been shown to be promising to improve routing performance in the context of intradomain routing. The applicability of SDN in inter-domain routing, especially with respect to route convergence, has not been properly explored. In this work, we propose a mathematical model to quantify the BGP convergence time for inter-domain routing by capturing only the essential components in BGP convergence process. Based on the model and some practical observations, we study how SDN may help to facilitate the interdomain routing. We further present a greedy algorithm that selects Autonomous Systems (ASes) for incremental SDN deployment with the objectives of minimizing the BGP convergence time. The simulation result based on the real world Internet topology confirms the effectiveness of our proposed algorithm. <s> BIB010 </s> A Survey on Efforts to Evolve the Control Plane of Inter-Domain Routing <s> SDN as an Enabling Technology <s> Software-defined networking (SDN) scheme decouples network control plane and data plane, which can improve the flexibility of traffic management in networks. OpenFlow is a promising implementation instance of SDN scheme and has been applied to enterprise networks and data center networks in practice. However, it has less effort to spread SDN control scheme over the Internet to conquer the ossification of inter-domain routing. In this paper, we further innovate to the SDN inter-domain routing inspired by the OpenFlow protocol. We apply SDN flow-based routing control to inter-domain routing and propose a fine-granularity inter-domain routing mechanism, named SDI (Software Defined Inter-domain routing). It enables inter-domain routing to support the flexible routing policy by matching multiple fields of IP packet header. We also propose a method to reduce redundant flow entries for inter-domain settings. And, we implement a prototype and deploy it on a multi-domain testbed. <s> BIB011 </s> A Survey on Efforts to Evolve the Control Plane of Inter-Domain Routing <s> SDN as an Enabling Technology <s> Software-defined networking (SDN) abstracts low-level network functionalities to simplify network management and reduce costs. The OpenFlow protocol implements the SDN concept by abstracting network communications as flows to be processed by network elements. In OpenFlow, the high-level policies are translated into network primitives called rules that are distributed over the network. While the abstraction offered by OpenFlow allows to potentially implement any policy, it raises the new question of how to define the rules and where to place them in the network while respecting all technical and administrative requirements. In this paper, we propose a comprehensive study of the so-called OpenFlow rules placement problem with a survey of the various proposals intending to solve it. Our study is multifold. First, we define the problem and its challenges. Second, we overview the large number of solutions proposed, with a clear distinction between solutions focusing on memory management and those proposing to reduce signaling traffic to ensure scalability. Finally, we discuss potential research directions around the OpenFlow rules placement problem. <s> BIB012 </s> A Survey on Efforts to Evolve the Control Plane of Inter-Domain Routing <s> SDN as an Enabling Technology <s> As opposed to the decentralized control logic underpinning the devising of the Internet as a complex bundle of box-centric protocols and vertically integrated solutions, the software-defined networking (SDN) paradigm advocates the separation of the control logic from hardware and its centralization in software-based controllers. These key tenets offer new opportunities to introduce innovative applications and incorporate automatic and adaptive control aspects, thereby, easing network management and guaranteeing the user’s quality of experience. Despite the excitement, SDN adoption raises many challenges including the scalability and reliability issues of centralized designs that can be addressed with the physical decentralization of the control plane. However, such physically distributed, but logically centralized systems bring an additional set of challenges. This paper presents a survey on SDN with a special focus on the distributed SDN control. Besides reviewing the SDN concept and studying the SDN architecture as compared to the classical one, the main contribution of this survey is a detailed analysis of state-of-the-art distributed SDN controller platforms which assesses their advantages and drawbacks and classifies them in novel ways (physical and logical classifications) in order to provide useful guidelines for SDN research and deployment initiatives. A thorough discussion on the major challenges of distributed SDN control is also provided along with some insights into emerging and future trends in that area. <s> BIB013 </s> A Survey on Efforts to Evolve the Control Plane of Inter-Domain Routing <s> SDN as an Enabling Technology <s> When developing a stateful application (e.g. a load balancer) for an OpenFlow network, it is mandatory that the applications receive a consistent view of the network state from the controller. However, when a burst of packets arrive in an OpenFlow switch and the default action is to send those packets to the controller (via Packet-In), a stateful application can be taken to an inconsistent state if the controller passes all those packets to the application. Previous works proposed the modification of the OpenFlow specification or in the switches in order to alter this default behavior. The main idea of this paper is to make some modifications in the controller software and to tune the parameters of the OpenFlow protocol to avoid inconsistency in OpenFlow applications state that required an appropriate treatment of multiple Packet-In events. The results indicate that the proposed scheme indeed delivers a consistent view of the network state for stateful OpenFlow applications. <s> BIB014
One of the major features of the BGP is the scalability of the protocol due to its fully-distributed nature. The size-effect of distributed control of the BGP is causing the protocol "chattiness" BIB002 and the long convergence time  , since every BGP speaker has to generate the global view of the network state to make decisions about routing. The centralization of inter-domain routing control has the potential to mitigate the BGP issues  BIB003 BIB007 . A bird's eye view of the centralized solution has the potential to identify misconfiguration, avoid route leaks, address the satisfaction and dissatisfaction among ASs BIB008 and understand and perform troubleshooting; all sorts of undesired network behavior will be exposed to the centralized control. With SDN technologies, the consistency of the network state is encouraged by the principle of logical centralization BIB013 . The inter-domain routing centralization has the potential to benefit the application of traffic engineering techniques, enforcement of routing policies, network troubleshooting and other desirable features. For example, the proposal of iSDX BIB009 uses the SDN centralized control in an IXP to allow the creation of more flexible forwarding policies, the reduction of the forwarding table size of OpenFlow devices used by the IXP participants and the end-to-end enforcing of QoS. The adoption of SDN technologies has the potential to solve the management decentralization problem of the traditional network, as discussed in BIB010 . Other previous proposals that use exclusively traditional network technologies BIB001  required extensions for the BGP or a brand new network protocol to make them operational. This results in a difficult scenario that is not easy to deploy or manage for ASs because of CAPEX, OPEX, security and reliability concerns. New network services can emerge if the current inter-domain routing system allows the evolution of the routing control plane. The traditional network mostly applies the decentralization of the routing decision, and with the advent of SDN concepts, the logical centralization of the routing control plane may enable inter-domain routing evolution. Thereby, a good question to pose regarding SDN is the following: Why have SDN technologies not yet changed the inter-domain landscape? First of all, it is worth noting that the SDN paradigm is a brand new approach to design networks (although it inherits ideas from other approaches BIB004 ), which is different from the traditional network that has been the main paradigm to construct networks since the Internet's inception. Thereby, the technologies that instantiate SDN concepts are in their early stages, and as they are not mature technologies, wide adoption is not expected. The most successful SDN technology is the OpenFlow protocol. This protocol has some hindrance regarding memory and signaling utilization  because OpenFlow switches usually use Ternary Content Addressable Memory (TCAM) as the main memory to match a flow. That type of memory is very fast, however having the drawback of being expensive with a high energy consumption. Therefore, the fine-grained OpenFlow rules can represent a cumbersome inter-domain environment where the number of prefixes (or flows) is tremendously high BIB011 . Flow management is almost mandatory for the real deployment of the OpenFlow protocol in inter-domain routing, and that problem can be understood as an extension of the rule placement problem inside OpenFlow networks. A detailed survey about flow management can be seen in the work of Nguyen et al. BIB012 . Another drawback of the OpenFlow networks is the reliability between controllers and the data plane elements (OpenFlow switches). Once the control and data plane is decoupled, when the control becomes unavailable, the forwarding elements may not continue to work appropriately. Some works claim that the data plane elements need to have some capabilities to fix those scenarios, and a mix of control and data plane programmability can be the key for future network solutions. Ideas for allowing data plane elements to become more flexible and programmable are in their infancy, such as P4 BIB005 or OpenState BIB006 , and those technologies could resolve the flexibility and performance of OpenFlow switches. Therefore, to be practical, an OpenFlow solution must manage the flows (installation, aggregation and eviction) and maintain a trade-off among rule installation and the signaling overhead between OpenFlow switches and the OpenFlow controller to maintain the availability of the network BIB012 BIB014 . For ASs, and especially ISPs, new proposals cannot be adopted for inter-domain routing that represent a risk (reliability, availability, performance, security and other requirements) to their business unless substantial profit is imminent BIB007 .