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

Fast emergency paths schema to overcome transient link failures in ospf routing

A reliable network infrastructure must be able to sustain traffic flows, even when a failure occurs and changes the network topology. During the occurrence of a failure, routing protocols, like OSPF, take from hundreds of milliseconds to various seconds in order to converge. During this convergence period, packets might traverse a longer path or even a loop. An even worse transient behaviour is that packets are dropped even though destinations are reachable. In this context, this paper describes a proactive fast rerouting approach, named Fast Emergency Paths Schema (FEP-S), to overcome problems originating from transient link failures in OSPF routing. Extensive experiments were done using several network topologies with different dimensionality degrees. Results show that the recovery paths, obtained by FEPS, are shorter than those from other rerouting approaches and can improve the network reliability by reducing the packet loss rate during the routing protocols convergence caused by a failure.Comment: 18 page

IP Fast Reroute with Remote Loop-Free Alternates: the Unit Link Cost Case

Up to not so long ago, Loop-Free Alternates (LFA) was the only viable option for providing fast protection in pure IP and MPLS/LDP networks. Unfortunately, LFA cannot provide protection for all possible failure cases in general. Recently, the IETF has initiated the Remote Loop-Free Alternates (rLFA) technique, as a simple extension to LFA, to boost the fraction of failure cases covered by fast protection. Before further stan- dardization and deployment, however, it is crucial to determine to what extent rLFA can improve the level of protection in a general IP network, as well as to find optimization methods to tweak a network for 100% rLFA coverage. In this paper, we take the first steps towards this goal by solving these problems in the special, but practically relevant, case when each network link is of unit cost. We also provide preliminary numerical evaluations conducted on real IP network topologies, which suggest that rLFA significantly improves the level of protection, and most networks need only 2 − 3 new links to be added to attain 100% failure case coverage

Segment Routing: a Comprehensive Survey of Research Activities, Standardization Efforts and Implementation Results

Fixed and mobile telecom operators, enterprise network operators and cloud providers strive to face the challenging demands coming from the evolution of IP networks (e.g. huge bandwidth requirements, integration of billions of devices and millions of services in the cloud). Proposed in the early 2010s, Segment Routing (SR) architecture helps face these challenging demands, and it is currently being adopted and deployed. SR architecture is based on the concept of source routing and has interesting scalability properties, as it dramatically reduces the amount of state information to be configured in the core nodes to support complex services. SR architecture was first implemented with the MPLS dataplane and then, quite recently, with the IPv6 dataplane (SRv6). IPv6 SR architecture (SRv6) has been extended from the simple steering of packets across nodes to a general network programming approach, making it very suitable for use cases such as Service Function Chaining and Network Function Virtualization. In this paper we present a tutorial and a comprehensive survey on SR technology, analyzing standardization efforts, patents, research activities and implementation results. We start with an introduction on the motivations for Segment Routing and an overview of its evolution and standardization. Then, we provide a tutorial on Segment Routing technology, with a focus on the novel SRv6 solution. We discuss the standardization efforts and the patents providing details on the most important documents and mentioning other ongoing activities. We then thoroughly analyze research activities according to a taxonomy. We have identified 8 main categories during our analysis of the current state of play: Monitoring, Traffic Engineering, Failure Recovery, Centrally Controlled Architectures, Path Encoding, Network Programming, Performance Evaluation and Miscellaneous...Comment: SUBMITTED TO IEEE COMMUNICATIONS SURVEYS & TUTORIAL

Route recovery schemes for link and node failure and link congestion

Link/Node failure occurs frequently causing service disruption in computer networks. Hardware techniques have been developed to protect the network from Link/Node failure. These techniques work in physical layer, therefore their convergence time is very small. On the other hand, many schemes have been proposed to mitigate the failure influence on the network. These schemes work in upper layers such as the network layer. However, hardware solutions faster than other schemes, but they are expensive. Link/Node failure causes all flows which were using the failed link/node are temporarily interrupted till a new path reestablished. Three recovery algorithms have been proposed that mitigate the changes occur in the network. These changes are link/node failure and link congestion. The algorithms mainly pre-compute a backup next hop for each destination in the network. This path is feasible to accommodate re-routed traffic when a failure occurs without causing congestion or loops. Simulations have been conducted to show the performance of the proposed algorithms using ns2 network simulation tool. The results show fast recovery for all flows were using the link/node failure. Furthermore, the throughput per node also increases due to decrease interruption service time

An automatic restoration scheme for switch-based networks

International audienceThis paper presents a fully automated distributed resilient routing scheme for switch-based or new generation router based networks. The failure treatment is done locally and other nodes in the network do not need to undertake special actions. In contrast to conventional IP routing schemes, each node routes the traffic on the basis of the entering arc and of the destination. The resulting constraint is that two flows to the same destination entering in a node by a common arc have to merge after this arc. It is shown that this is sufficient for dealing with all single link failure situations, assuming that the network is symmetric and two-link connected. Two heuristic approaches are proposed to handle the corresponding dimensioning problem for large network instances. The proposed method generalizes some methods of literature [6], [8] and provides more cost-efficient solutions

Openflow Path Fast Failover Fast Convergence Mechanism

Whenever there is a link failure in the network, OpenFlow controller can react by computing a new backup path and provide the information to the affected node or the node can switch to backup path locally using the predefined backup path table provided by the OpenFlow controller. Setting predefined backup paths, results in a faster network rerouting time compared to backup path that establish on demand. However, it may lead to the use of sub-optimal backup path. In this paper, we present a fast and efficient failover mechanism for redirecting traffic flows to more optimal backup path when there is a link failure or congestion problem. We introduce a switch flow entry expiry mechanism to immediately reroute traffic to backup path to reduce the network restoration time. To update the switch with more optimal path information, the controller require a round trip to the network and this can introduce to slow network convergence. We proposed a local pre-calculated path dataset mechanism in Openflow controller to allow fast network convergence

Efficient Routing Protection Algorithm Based on Optimized Network Topology

Network failures are unavoidable and occur frequently. When the network fails, intra-domain routing protocols deploying on the Internet need to undergo a long convergence process. During this period, a large number of messages are discarded, which results in a decline in the user experience and severely affects the quality of service of Internet Service Providers (ISP). Therefore, improving the availability of intra-domain routing is a trending research question to be solved. Industry usually employs routing protection algorithms to improve intra-domain routing availability. However, existing routing protection schemes compute as many backup paths as possible to reduce message loss due to network failures, which increases the cost of the network and impedes the methods deployed in practice. To address the issues, this study proposes an efficient routing protection algorithm based on optimized network topology (ERPBONT). ERPBONT adopts the optimized network topology to calculate a backup path with the minimum path coincidence degree with the shortest path for all source purposes. Firstly, the backup path with the minimum path coincidence with the shortest path is described as an integer programming problem. Then the simulated annealing algorithm ERPBONT is used to find the optimal solution. Finally, the algorithm is tested on the simulated topology and the real topology. The experimental results show that ERPBONT effectively reduces the path coincidence between the shortest path and the backup path, and significantly improves the routing availability

Fast network configuration in Software Defined Networking

Software Defined Networking (SDN) provides a framework to dynamically adjust and re-program the data plane with the use of flow rules. The realization of highly adaptive SDNs with the ability to respond to changing demands or recover after a network failure in a short period of time, hinges on efficient updates of flow rules. We model the time to deploy a set of flow rules by the update time at the bottleneck switch, and formulate the problem of selecting paths to minimize the deployment time under feasibility constraints as a mixed integer linear program (MILP). To reduce the computation time of determining flow rules, we propose efficient heuristics designed to approximate the minimum-deployment-time solution by relaxing the MILP or selecting the paths sequentially. Through extensive simulations we show that our algorithms outperform current, shortest path based solutions by reducing the total network configuration time up to 55% while having similar packet loss, in the considered scenarios. We also demonstrate that in a networked environment with a certain fraction of failed links, our algorithms are able to reduce the average time to reestablish disrupted flows by 40%