Multipath inter-domain policy routing

Dissertação submetida para a obtenção do grau de Doutor em Engenharia Electrotécnica e de ComputadoresRouting can be abstracted to be a path nding problem in a graph that models the network. The problem can be modelled using an algebraic approach that describes the way routes are calculated and ranked. The shortest path problem is the most common form and consists in nding the path with the smallest cost. The inter-domain scenario introduces some new challenges to the routing problem: the routing is performed between independently con gured and managed networks; the ranking of the paths is not based on measurable metrics but on policies; and the forwarding is destination based hop-by-hop. In this thesis we departed from the Border gateway Protocol (BGP) identifying its main problems and elaborating on some ideal characteristics for a routing protocol suited for the inter-domain reality. The main areas and contributions of this work are the following: The current state of the art in algebraic modeling of routing problems is used to provide a list of possible alternative conditions for the correct operation of such protocols. For each condition the consequences in terms of optimality and network restrictions are presented. A routing architecture for the inter-domain scenario is presented. It is proven that it achieves a multipath routing solution in nite time without causing forwarding loops. We discuss its advantages and weaknesses. A tra c-engineering scheme is designed to take advantage of the proposed architecture. It works using only local information and cooperation of remote ASes to minimize congestion in the network with minimal signalling. Finally a general model of a routing protocol based on hierarchical policies is used to study how e cient is the protocol operation when the correctness conditions are met. This results in some conclusions on how the policies should be chosen and applied in order to achieve speci c goals.Portuguese Science and Technology Foundation -(FCT/MCTES)grant SFRH/BD/44476/2008; CTS multi-annual funding project PEst OE/EEI/UI0066/2011; MPSat project PTDC/EEA TEL/099074/2008; OPPORTUNISTICCR project PTDC/EEA-TEL/115981/2009; Fentocells project PTDC/EEA TEL/120666/201

TOPOLOGY CONTROL ALGORITHMS FOR RULE-BASED ROUTING

In this dissertation, we introduce a new topology control problem for rule- based link-state routing in autonomous networks. In this context, topology control is a mechanism to reduce the broadcast storm problem associated with link-state broadcasts. We focus on a class of topology control mechanisms called local-pruning mechanisms. Topology control by local pruning is an interesting multi-agent graph optimization problem, where every agent/router/station has access to only its local neighborhood information. Every agent selects a subset of its incident link-state in- formation for broadcast. This constitutes the pruned link-state information (pruned graph) for routing. The objective for every agent is to select a minimal subset of the local link-state information while guaranteeing that the pruned graph preserves desired paths for routing. In topology control for rule-based link-state routing, the pruned link-state information must preserve desired paths that satisfy the rules of routing. The non- triviality in these problems arises from the fact that the pruning agents have access to only their local link-state information. Consequently, rules of routing must have some property, which allows specifying the global properties of the routes from the local properties of the graph. In this dissertation, we illustrate that rules described as algebraic path problem in idempotent semirings have these necessary properties. The primary contribution of this dissertation is identifying a policy for pruning, which depends only on the local neighborhood, but guarantees that required global routing paths are preserved in the pruned graph. We show that for this local policy to ensure loop-free pruning, it is sufficient to have what is called an inflatory arc composition property. To prove the sufficiency, we prove a version of Bellman's optimality principle that extends to path-sets and minimal elements of partially ordered sets. As a motivating example, we present a stable path topology control mecha- nism, which ensures that the stable paths for routing are preserved after pruning. We show, using other examples, that the generic pruning works for many other rules of routing that are suitably described using idempotent semirings

Planning and verification of multipath routing protocols

Conventionally the problem of the best path in a network refers to the shortest path problem. However, for the vast majority of networks present nowadays this solution has some limitations which directly affect their proper functioning, as well as an inefficient use of their potentialities. Problems at the level of large networks where graphs of high complexity are commonly present as well as the appearing of new services and their respective requirements, are intrinsically related to the inability of this solution. In order to overcome the needs present in these networks, a new approach to the problem of the best path must be explored. One solution that has aroused more interest in the scientific community considers the use of multiple paths between two network nodes, where they can all now be considered as the best path between those nodes. Therefore, the routing will be discontinued only by minimizing one metric, where only one path between nodes is chosen, and shall be made by the selection of one of many paths, thereby allowing the use of a greater diversity of the present paths (obviously, if the network consents). The establishment of multi-path routing in a given network has several advantages for its operation. Its use may well improve the distribution of network traffic, improve recovery time to failure, or it can still offer a greater control of the network by its administrator. These factors still have greater relevance when networks have large dimensions, as well as when their constitution is of high complexity, such as the Internet, where multiple networks managed by different entities are interconnected. A large part of the growing need to use multipath protocols is associated to the routing made based on policies. Therefore, paths with different characteristics can be considered with equal level of preference, and thus be part of the solution for the best way problem. To perform multi-path routing using protocols based only on the destination address has some limitations but it is possible. Concepts of graph theory of algebraic structures can be used to describe how the routes are calculated and classified, enabling to model the routing problem. This thesis studies and analyzes multi-path routing protocols from the known literature and derives a new algebraic condition which allows the correct operation of these protocols without any network restriction. It also develops a range of software tools that allows the planning and the respective verification/validation of new protocols models according to the study made

An algebraic perspective on the convergence of vector-based routing protocols

This thesis studies the properties of vector-based routing protocols whose underlying algebras are strictly increasing. Strict increasingness has previously been shown to be both a sufficient and a necessary condition for the convergence of path-vector protocols. One of the key contributions of this thesis is to link vector-based routing to a much larger family of asynchronous iterative algorithms. This unlocks a significant body of existing theory, and allows asynchronous protocols to be proved correct by purely synchronous reasoning. As well as applying it to routing protocols, this thesis advances the asynchronous theory in two ways. Firstly it shows that the existing conditions required for convergence may be relaxed. Secondly it proposes the first model for ``dynamic'' asynchronous processes in which both the problem being solved and the set of participants change over time. The thesis' attention then turns to models of routing problems, and presents a new algebraic structure that is simpler and more expressive than the state of the art. In particular this structure is capable of modelling routing problems that underlie both distance-vector and path-vector protocols. Consequently these two families of vector-based protocols may be unified for the first time. The new structure is also capable of modelling protocols that use path-dependent conditional policy. Next the work above is used to construct a model of an abstract vector-based protocol. This is then used in the first proof of correctness for strictly increasing distance-vector protocols and a new proof of correctness for strictly increasing path-vector protocols. The latter is an improvement over previous results as it i) proves that convergence is deterministic ii) does not assume reliable communication between nodes and iii) applies to path-vector protocols with path-dependent conditional policy. The long standing question of the worst-case rate of convergence for a strictly increasing path-vector protocol is then answered by lowering the previous upper bound of $O(n!)$ to a new tight bound of~$\Theta(n^2)$. Finally all of the work has been formalised in the proof assistant Agda. Not only does this significantly increase users' confidence in the validity of the results, the resulting Agda library may also be used to verify the correctness of protocol implementations. To illustrate this, a formal proof of correctness is described for a path-vector protocol which contains many of the features of the Border Gateway Protocol including: local preferences, communities, an expressive conditional policy language and path inflation.EPSRC Doctoral Training gran

Local Pruning for Information Dissemination in Dynamic Networks for Solving the Idempotent Semiring Algebraic Path Problem

We present a method, inspired from routing in dynamic data networks, to solve the Semiring Algebraic Path Problem (SAPP) for dynamic graphs. The method can be used in dynamic networks such as Mobile Ad Hoc Networks, where the network link states are highly dynamic. The algorithm makes use of broadcasting as primary mechanism to recompute the SAPP solution. The solution suffers from broadcast storm problems, and we propose a selective broadcasting mechanism that reduces the broadcast storm. We call this method local pruning and prove its correctness

Multipath policy routing in packet switched networks

Dissertação apresentada para obtenção do Grau de Mestre em Engenharia Electrotécnica e de Computadores, pela Universidade Nova de Lisboa, Faculdade de Ciências e TecnologiaNowadays, the continuous operations of large networks, under multiple ownerships, are of tremendous importance and as a result, routing protocols have gained numerous extensions and accumulated complexity. Policy-based routing can be of signi cance for common networks when the cost of transporting a bit is no longer the biggest pressure point. The best path problem is a generalization of the shortest path problem that suits policy based routing. This means that preferences for the paths depend on semantically rich characteristics, in which two di erent paths may have the same preference. However, current policy-based routing models cannot take full advantage of the multiplicity of connections to a given destination and are single path in nature. Therefore multipath can bring several advantages in policy based routing. Designing multipath routing protocols based on policies seem to be a problem of interest. To model routing problems, algebraic structures and graph theory are used. Through variants of classical methods of linear algebra routing problems can be solved. The objective of this dissertation is to devise a multipath policy-based routing protocol using a simple destination-based hop-by-hop protocol with independent forwarding decisions. Networks featuring these characteristics can be more resilient to failures, provide better tra c distribution and maintain a simple forwarding paradigm. The dissertation concludes with the trade-o 's between the exibility of the proposed solution, the amount of multiple paths that can be used simultaneously and the network restrictions that must be applied

Algebraic and Geometric Models for Space Networking

In this paper we introduce some new algebraic and geometric perspectives on networked space communications. Our main contribution is a novel definition of a time-varying graph (TVG), defined in terms of a matrix with values in subsets of the real line P(R). We leverage semi-ring properties of P(R) to model multi-hop communication in a TVG using matrix multiplication and a truncated Kleene star. This leads to novel statistics on the communication capacity of TVGs called lifetime curves, which we generate for large samples of randomly chosen STARLINK satellites, whose connectivity is modeled over day-long simulations. Determining when a large subsample of STARLINK is temporally strongly connected is further analyzed using novel metrics introduced here that are inspired by topological data analysis (TDA). To better model networking scenarios between the Earth and Mars, we introduce various semi-rings capable of modeling propagation delay as well as protocols common to Delay Tolerant Networking (DTN), such as store-and-forward. Finally, we illustrate the applicability of zigzag persistence for featurizing different space networks and demonstrate the efficacy of K-Nearest Neighbors (KNN) classification for distinguishing Earth-Mars and Earth-Moon satellite systems using time-varying topology alone.Comment: 43 pages, 18 figures, comments welcom

Um estudo de algoritmos de gestão de tráfego de baixa complexidade em SDNs

A falta de soluções que consigam responder às necessidades das redes atuais gera uma má gestão do tráfego que origina situações de congestionamento quando ainda existem partes da rede livres. Nas redes tradicionais cada nó apenas consegue determinar qual o próximo nó para qual o tráfego deve ser encaminhado, esta característica aliada à falta de conhecimento global da rede torna a tarefa de otimizar o custo das ligações difícil, sendo complexo a obtenção de uma solução ótima. O uso de Software-Defined Networking traz vantagens que permitem contornar as adversidades das redes tradicionais, tornando-se possível desenhar novos métodos de encaminhamento de tráfego, mais eficientes e que considerem o estado global da rede. Aliar estas vantagens ao uso de novos métodos de encaminhamento poderá traduzir-se numa melhoria do desempenho das redes, como por exemplo conseguir um aumento na eficiência no transporte de dados. A separação do plano de controlo resulta em algumas condicionantes de escalabilidade que condicionam a utilização de métodos de distribuição de tráfego baseados em otimização. As duas condicionantes principais são o número de regras suportadas pelos equipamentos e o custo da comunicação entre os equipamentos na rede e o controlador. Este trabalho parte de uma arquitetura que tem essas limitações em conta, onde a eficiência da utilização da rede depende de dois fatores: o cálculo de caminhos na rede e a distribuição de tráfego por esses mesmos caminhos. Nesta dissertação são estudadas novas abordagens aos métodos de cálculo de caminhos entre os nós de acesso e aos métodos de distribuição de tráfego tradicionais, focando-se no desenvolvimento de uma ferramenta de modelação teórica que permite estudar as várias alternativas aos métodos de encaminhamento tradicionais fornecendo um indicador de desempenho referente ao método estudado. Foram realizadas várias experiências que demonstram o impacto no transporte de dados de diferentes métodos de encaminhamento

Routing at Large Scale: Advances and Challenges for Complex Networks

International audienceA wide range of social, technological and communication systems can be described as complex networks. Scale-free networks are one of the well-known classes of complex networks in which nodes degree follow a power-law distribution. The design of scalable, adaptive and resilient routing schemes in such networks is very challenging. In this article we present an overview of required routing functionality, categorize the potential design dimensions of routing protocols among existing routing schemes and analyze experimental results and analytical studies performed so far to identify the main trends/trade-offs and draw main conclusions. Besides traditional schemes such as hierarchical/shortest-path path-vector routing, the article pays attention to advances in compact routing and geometric routing since they are known to significantly improve the scalability in terms of memory space. The identified trade-offs and the outcomes of this overview enable more careful conclusions regarding the (in-)suitability of different routing schemes to large-scale complex networks and provide a guideline for future routing research