Real ISP Network Research Articles

SDN-Based Privacy Preserving Cross Domain Routing

Today's large-scale enterprise networks, data center networks, and wide area networks can be decomposed into multiple administrative or geographical domains. Domains may be owned by different administrative units or organizations. Hence protecting domain information is an important concern. Existing general-purpose Secure Multi-Party Computation (SMPC) methods that preserves privacy for domains are extremely slow for cross-domain routing problems. In this paper we present PYCRO, a cryptographic protocol specifically designed for privacy-preserving cross-domain routing optimization in Software Defined Networking (SDN) environments. PYCRO provides two fundamental routing functions, policy-compliant shortest path computing and bandwidth allocation, while ensuring strong protection for the private information of domains. We rigorously prove the privacy guarantee of our protocol. To improve time efficiency we design the QuIck Pathing (QIP) technique. QIP only requires one-time offline preprocessing and very fast online computation. We have implemented a prototype system that runs PYCRO and QIP on servers in a campus network. Experimental results using real ISP network topologies show that PYCRO and QIP are very efficient in computation and communication costs.

Load-balanced overlay recovery scheme with delay minimisation

Recovery from a link or node failure in the internet is often subjected to seconds or minutes of routing convergence, during which certain end-to-end connections may experience seconds or minutes of outage. According to this problem, existing approaches reroute the data traffic to a pre-defined backup path to detour the failed components. However, the maintenance of backup path increases the significant bandwidth expenditure. On the other hand, the diverted traffic may cause congestion on the backup path if it is not carefully split over multiple paths according to their available capacity. In this paper, we propose an efficient recovery scheme by using one-hop overlay multipath source routing, which is a post-failure recovery method. Once a failure happens, multiple one-hop overlay paths are constructed by selecting strategically multiple relay nodes, and the affected traffic is diverted to these paths in a well-balanced manner. We formulate the traffic allocation problem as a tractable linear programming (LP) optimisation problem, whose goal is to minimise the worse-case network congestion ratio. Simulations based on a real ISP network and a synthetic internet topology show that our scheme can effectively balance link utilisation dramatically and improve the reliability of network.

Load-balanced overlay recovery scheme with delay minimisation

Recovery from a link or node failure in the internet is often subjected to seconds or minutes of routing convergence, during which certain end-to-end connections may experience seconds or minutes of outage. According to this problem, existing approaches reroute the data traffic to a pre-defined backup path to detour the failed components. However, the maintenance of backup path increases the significant bandwidth expenditure. On the other hand, the diverted traffic may cause congestion on the backup path if it is not carefully split over multiple paths according to their available capacity. In this paper, we propose an efficient recovery scheme by using one-hop overlay multipath source routing, which is a post-failure recovery method. Once a failure happens, multiple one-hop overlay paths are constructed by selecting strategically multiple relay nodes, and the affected traffic is diverted to these paths in a well-balanced manner. We formulate the traffic allocation problem as a tractable linear programming (LP) optimisation problem, whose goal is to minimise the worse-case network congestion ratio. Simulations based on a real ISP network and a synthetic internet topology show that our scheme can effectively balance link utilisation dramatically and improve the reliability of network.

The role of the inter-controller consensus in the placement of distributed SDN controllers

We consider a distributed Software Defined Networking (SDN) architecture adopting a cluster of controllers to improve network scalability and reliability. Different from previous works that focused solely on the control traffic exchanged between controllers and switches, we additionally consider the control traffic exchanged among the controllers (e.g., the control traffic to keep the shared data structures synchronized). We advocate a careful placement of the controllers, which should take into account both the two kinds of control traffic. We evaluate, for some real ISP network topologies, the delay tradeoffs for the controller placement problem and we propose a novel evolutionary algorithm to find the corresponding Pareto frontier. Furthermore, we develop a simple model to estimate the reaction time perceived by the switches, which is accurately validated in an operational Software Defined WAN (SDWAN). We also formalize the optimization problem to minimize the reaction time and devise a novel approximation algorithm, whose performance is assessed against the optimal solver in real ISP network topologies.Our work provides novel quantitative tools to optimize the planning and the design of the network supporting the control plane of SDN networks, especially when the network is very large and in-band control plane is adopted. We also show that for operationally distributed controllers (e.g., OpenDaylight and ONOS), the location of the controller that acts as leader in the consensus algorithm has a strong impact on the reactivity perceived by the switches.

Resilient Routing Overlay Network Construction with Super-Relay Nodes

Overlay routing has emerged as a promising approach to improve reliability and efficiency of the Internet. The key to overlay routing is the placement and maintenance of the overlay infrastructure, especially, the selection and placement of key relay nodes. Spurred by the observation that a few relay nodes with high betweenness centrality can provide more optimal routes for a large number of node pairs, we propose a resilient routing overlay network construction method by introducing Super-Relay nodes. In detail, we present the K-Minimum Spanning Tree with Super-Relay nodes algorithm (SR-KMST), in which we focus on the selection and connection of Super-Relay nodes to optimize the routing quality in a resilient and scalable manner. For the simultaneous path failures between the default physical path and the overlay backup path, we also address the selection of recovery path. The objective is to select a proper one-hop recovery path with minimum cost in path probing and measurement. Simulations based on a real ISP network and a synthetic Internet topology show that our approach can provide high-quality overlay routing service, while achieving good robustness.

Freezing forwarding functionality to make the network greener

This work proposes a novel approach to reduce the power consumption of IP routers: freezing the forwarding engine of routers line-cards. In fact, recent studies showed that about 60% of the power consumption of a line-card is wasted to lookup the routing table during packet forwarding process. We first define the proposed approach, called Freezing Forwarding Functionality (F3). Then, we provide an ILP formulation of the energy minimization problem under F3mode and define a heuristic algorithm, referred to as Green Backbone Algorithm (GBA), to solve the problem in large networks. The performance of GBA is evaluated under different traffic scenarios in real ISP network topologies, and a comparison with the ILP solution is carried out for small networks. Results show that: (i) GBA performance, in terms of number of nodes in F3mode, are very close to optimal ILP solution ones; (ii) a large energy saving (up to 80% of nodes in F3mode ) is obtained in large networks during low traffic hours; (iii) a limited impact on paths length increase is achieved.

Cross-Layer Approach for Minimizing Routing Disruption in IP Networks

Backup paths are widely used in IP networks to protect IP links from failures. However, existing solutions such as the commonly used independent model and Shared Risk Link Group (SRLG) model do not accurately reflect the correlation between IP link failures, and thus may not choose reliable backup paths. We propose a cross-layer approach for minimizing routing disruption caused by IP link failures. We develop a probabilistically correlated failure (PCF) model to quantify the impact of IP link failure on the reliability of backup paths. With the PCF model, we propose an algorithm to choose multiple reliable backup paths to protect each IP link. When an IP link fails, its traffic is split onto multiple backup paths to ensure that the rerouted traffic load on each IP link does not exceed the usable bandwidth. We evaluate our approach using real ISP networks with both optical and IP layer topologies. Experimental results show that two backup paths are adequate for protecting a logical link. Compared with existing works, the backup paths selected by our approach are at least 18 percent more reliable and the routing disruption is reduced by at least 22 percent. Unlike prior works, the proposed approach prevents the rerouted traffic from interfering with normal traffic.

Load-Balanced One-hop Overlay Multipath Routing with Path Diversity

Overlay routing has emerged as a promising approach to improve reliability and efficiency of the Internet. For one-hop overlay source routing, when a given primary path suffers from the link failure or performance degradation, the source can reroute the traffic to the destination via a strategically placed relay node. However, the over-heavy traffic passing through the same relay node may cause frequent package loss and delay jitter, which can degrade the throughput and utilization of the network. To overcome this problem, we propose a Load-Balanced One-hop Overlay Multipath Routing algorithm (LB-OOMR), in which the traffic is first split at the source edge nodes and then transmitted along multiple one-hop overlay paths. In order to determine an optimal split ratio for the traffic, we formulate the problem as a linear programming (LP) formulation, whose goal is to minimize the worse-case network congestion ratio. Since it is difficult to solve this LP problem in practical time, a heuristic algorithm is introduced to select the relay nodes for constructing the disjoint one-hop overlay paths, which greatly reduces the computational complexity of the LP algorithm. Simulations based on a real ISP network and a synthetic Internet topology show that our proposed algorithm can reduce the network congestion ratio dramatically, and achieve high-quality overlay routing service.

An OSPF-Integrated Routing Strategy for QoS-Aware Energy Saving in IP Backbone Networks

This paper deals with an energy saving routing solution, called Energy Saving IP Routing (ESIR), to be applied in an IP network. ESIR operation is integrated with Open Shorthest Path First (OSPF) protocol and allows the selection of the links to be switched off so that the negative effects of the IP topology reconfiguration procedures are avoided. The basic mechanisms which ESIR is based on are the concepts of SPT exportation and move. These mechanisms allow to share a Shortest Path Tree (SPT) between neighbor routers, so that the overall set of active network links can be reduced. Properties of moves are defined and the energy saving problem in an IP network is formulated as the problem of finding the Maximum Set of Compatible Moves (MSCM). The MSCM problem is investigated in two steps: firstly, a relaxed version of the problem, named basic MSCM problem, is considered in which QoS requirements are neglected; in the second step, the solution of the full problem, named QoS-aware MSCM problem, is faced. We prove that the basic MSCM problem can be formulated as the well-known Maximum Clique Problem in a graph; instead the QoS-aware MSCM introduces a condition equivalent to the Knapsack problem. ILP formulations to solve both the problems are given and heuristics to solve them in practical cases are proposed. The performance evaluation shows that in a real ISP network scenario ESIR is able to switch off up to 30% of network links by exploiting over-provisioning adopted by operators in the network resource planning phase and typical daily traffic trend.

Network sensitivity to hot-potato disruptions

Hot-potato routing is a mechanism employed when there are multiple (equally good) interdomain routes available for a given destination. In this scenario, the Border Gateway Protocol (BGP) selects the interdomain route associated with the closest egress point based upon intradomain path costs. Consequently, intradomain routing changes can impact interdomain routing and cause abrupt swings of external routes, which we call hot-potato disruptions . Recent work has shown that hot-potato disruptions can have a substantial impact on large ISP backbones and thereby jeopardize the network robustness. As a result, there is a need for guidelines and tools to assist in the design of networks that minimize hot-potato disruptions. However, developing these tools is challenging due to the complex and subtle nature of the interactions between exterior and interior routing. In this paper, we address these challenges using an analytic model of hot-potato routing that incorporates metrics to evaluate network sensitivity to hot-potato disruptions. We then present a methodology for computing these metrics using measurements of real ISP networks. We demonstrate the utility of our model by analyzing the sensitivity of a large AS in a tier~1 ISP network.

Stability issues in OSPF routing

We study the stability of the OSPF protocol under steady state and perturbed conditions. We look at three indicators of stability, namely, (a) network convergence times, (b) routing load on processors, and (c) the number of route flaps. We study these statistics under three different scenarios: (a) on networks that deploy OSPF with TE extensions, (b) on networks that use subsecond HELLO timers, and (c) on networks that use alternative strategies for refreshing link-state information. Our results are based on a very detailed simulation of a real ISP network with 292 nodes and 765 links.