Optimizing IGP Link Costs for Improving IP-level Resilience

Recently, major vendors have introduced new router platforms to the market that support fast IP-level failure pro- tection out of the box. The implementations are based on the IP Fast ReRoute–Loop Free Alternates (LFA) standard. LFA is simple, unobtrusive, and easily deployable. This simplicity, however, comes at a severe price, in that LFA usually cannot protect all possible failure scenarios. In this paper, we give new graph theoretical tools for analyzing LFA failure case coverage and we seek ways for improvement. In particular, we investigate how to optimize IGP link costs to maximize the number of protected failure scenarios, we show that this problem is NP- complete even in a very restricted formulation, and we give exact and approximate algorithms to solve it. Our simulation studies show that a deliberate selection of IGP costs can bring many networks close to complete LFA-based protection

Otimização de redes IP com mecanismos de reencaminhamento rápido

Mestrado em Engenharia de Computadores e TelemáticaThis dissertation studies strategies for assigning costs to the interfaces of routers inside an IP network to potentiate the use of Loop-Free Alternates (LFA). LFA is a fast reroute mechanism that has been recently deployed in commercial routers. This mechanism allows routers to forward traffic through alternative paths right after the detection of a network failure, avoiding a higher loss of packets during the network’s recovery process. The problem is that this mechanism does not usually provide coverage to all possible failures. Moreover, repair paths may lead to congestion and even forwarding loops. An application was developed that, given a network topology and its supporting traffic matrix, allows to find IGP costs that improve the network performance when employing this mechanism. The implemented strategies try to minimize situations where the use of repair paths leads to micro-loops or link overloads, thus preserving the quality of the service. The computational results show that it is possible to minimize the effects of a failure through an intelligent choice of costs. It is also possible to conclude that, for the majority of cases, increasing the LFA coverage of a network is not the best strategy. Depending on the available resources, it becomes often necessary to sacrifice this coverage to obtain better performance levels.Esta dissertação estuda estratégias para a atribuição de custos IGP às interfaces dos routers de uma rede IP de forma a potenciar o uso de Loop-Free Alternates (LFA), um mecanismo de reencaminhamento rápido que tem sido recentemente implementado em routers comerciais. Este mecanismo permite que os routers reencaminhem tráfego por rotas alternativas assim que uma falha de rede é detetada, evitando uma maior perda de pacotes durante o período de recuperação da rede. O problema é que este mecanismo geralmente não oferece cobertura para todas as falhas possíveis. Além disso, as rotas de restauro podem causar congestão na rede e até mesmo ciclos de encaminhamento. Foi então desenvolvida uma aplicação que, dada uma topologia de rede e respetiva matriz de tráfego, permite determinar custos que melhorem o desempenho da rede quando emprega este mecanismo. As estratégias implementadas procuram minimizar situações em que o uso das rotas de restauro provoca ciclos de encaminhamento ou sobrecarga das ligações, preservando desta forma a qualidade da maior parte do serviço. Os resultados obtidos mostram que é possível minimizar os efeitos de uma falha através de uma escolha inteligente dos custos. Também é possível concluir que, na grande maioria dos casos, aumentar de forma cega a cobertura da rede através de Loop-Free Alternates não é a melhor estratégia. Dependendo dos recursos disponíveis, torna-se muitas vezes necessário sacrificar essa cobertura para obter melhores níveis globais de desempenho

Comparison of New Solutions in IP Fast Reroute

Currently, network requirements are placed on the efficiency and size of the networks. These conditions can be ensured by modern converged networks that integrate the functions of both data and telecommunication networks. Line or router failures have always been a part of transmission networks, which is no different from converged networks. As a result of outages, which can take from ms to tens of seconds, packets are lost. These outages cause degraded transmission quality, which is undesirable when transmitting real-time multimedia services (Voice over IP, video). To solve the mentioned problems, the IETF organization has developed IP Fast Reroute mechanisms to minimise the time to restore the connection after a line or node failure and, consequently, less packet loss. The article reviews and compares the latest IP Fast Reroute mechanisms deployed in the last three years. First, we have Optimistic Fast Rerouting, which calculates optimistic and fallback scenarios. The second is Post-processing Fast Reroute, which decomposes the network according to metrics such as load and route length. Third, Local Fast Reroute focused on low congestion and random access

Resilient and Scalable Forwarding for Software-Defined Networks with P4-Programmable Switches

Traditional networking devices support only fixed features and limited configurability. Network softwarization leverages programmable software and hardware platforms to remove those limitations. In this context the concept of programmable data planes allows directly to program the packet processing pipeline of networking devices and create custom control plane algorithms. This flexibility enables the design of novel networking mechanisms where the status quo struggles to meet high demands of next-generation networks like 5G, Internet of Things, cloud computing, and industry 4.0. P4 is the most popular technology to implement programmable data planes. However, programmable data planes, and in particular, the P4 technology, emerged only recently. Thus, P4 support for some well-established networking concepts is still lacking and several issues remain unsolved due to the different characteristics of programmable data planes in comparison to traditional networking. The research of this thesis focuses on two open issues of programmable data planes. First, it develops resilient and efficient forwarding mechanisms for the P4 data plane as there are no satisfying state of the art best practices yet. Second, it enables BIER in high-performance P4 data planes. BIER is a novel, scalable, and efficient transport mechanism for IP multicast traffic which has only very limited support of high-performance forwarding platforms yet. The main results of this thesis are published as 8 peer-reviewed and one post-publication peer-reviewed publication. The results cover the development of suitable resilience mechanisms for P4 data planes, the development and implementation of resilient BIER forwarding in P4, and the extensive evaluations of all developed and implemented mechanisms. Furthermore, the results contain a comprehensive P4 literature study. Two more peer-reviewed papers contain additional content that is not directly related to the main results. They implement congestion avoidance mechanisms in P4 and develop a scheduling concept to find cost-optimized load schedules based on day-ahead forecasts