In SDN, forwarding rules are frequently updated to adapt to network dynamics. During the procedure, path consistency needs to be preserved; otherwise, in-flight packets might meet with forwarding errors such as loops and black holes. Despite a large number of suggestions have been proposed, they take either a long duration or have high rule-space overheads, thus fail to be practical for large-scale high dynamic networks. In this paper, we propose FLUS, a Segment Routing (SR) based mechanism, to achieve fast and lightweight path updates. Basically, when a route needs a change, FLUS instantly employs SR to construct its desired new path by concatenating some fragments of the already existing paths. After the actual paths are established, FLUS then shifts incoming packets to them and disables the transitional ones. Such a design helps packets enjoy their new paths immediately without introducing rule-space overheads. This paper presents FLUS's segment allocation, path construction, and the corresponding optimal algorithms in detail. Our evaluation based on real and synthesized networks shows: FLUS can handle up to 92-100% updates using SR in real-time and save 72-88% rule overhead compared to prior methods.

As the network infrastructure has been consuming more and more power, various schemes have been proposed to improve the power efficiency of network devices. Many schemes put links to sleep when idle and wake them up when needed. A presumption in these schemes, though, is that router's line cards can be waken up very quickly. However, through systematic measurement of a major vendor's high-end routers, we find that it takes minutes to get a line card ready under the current design. To address this issue, we propose a new line card design that 1) keeps the host processor in a line card standby, which only consumes a small fraction of power but will save considerable wakeup time, and 2) downloads a slim slot of popular prefixes with higher priority, so that the line card will be ready for forwarding most of the traffic much earlier. We design algorithms as well as architecture that ensure fast and correct longest prefix match during prioritized routing prefix download. Experiments on an FPGA-based prototype show that the customized hardware can be ready to forward packets in 127.27 ms, which is 0.3% of the time the original design takes. This can better support numerous power-saving schemes based on the sleep/wakeup mechanism.

Migration of traffic from one configuration to another is common in SDNs due to node/link failures, network maintenance, policy reconfiguration, intrusion detection, network upgrades, and etc. When the network devices are informed by the controller to execute the traffic migration, it's difficult even impossible to force all network devices to perform the update action in a strict synchronized way. Thus the network is likely to see transient overlapped traffic from both the new configuration and the old one. This kind of overlap may cause overload to those hot spots. This paper reveals the transient congestion problem during traffic migration in an SDN update. According to the observation, it's feasible for the controller to schedule ingress nodes to perform the migration in an order thus the transient congestion is avoided. This scheduling problem is formulated as a Mixed Integer Linear Program (MIP) model. If feasible orders exist for ingress network nodes to perform the migration, the MIP can always find the order that achieves the minimum steps in all possibilities. A heuristic method (named ATOMIP (ATOmic-MIP)) is proposed to speed-up the solving of this MIP. Evaluation based on network topologies observed from real ISPs shows that the lossless migration happens in sub-seconds.

Current network infrastructures exhibit poor power efficiency, running network devices at full capacity all the time regardless of the traffic demand and distribution over the network. Most research on router power management are at component level or link level, treating routers as isolated devices. A complementary approach is to facilitate power management at network level by routing traffic through different paths to adjust the workload on individual routers or links. Given the high path redundancy and low link utilization in today's large networks, this approach can potentially allow more network devices or components to go into power saving mode. This paper proposes an intra-domain traffic engineering mechanism, GreenTE, which maximizes the number of links that can be put into sleep under given performance constraints such as link utilization and packet delay. Using network topologies and traffic data from several wide-area networks, our evaluation shows that GreenTE can reduce line-cards' power consumption by 27% to 42% under constraints that the maximum link utilization is below 50% and the network diameter remains the same as in shortest path routing.

False routing announcements are a serious security problem, which can lead to widespread service disruptions in the Internet. A number of detection systems have been proposed and implemented recently, however, it takes time to detect attacks, notify operators, and stop false announcements. Thus detection systems should be complemented by a mitigation scheme that can protect data delivery before the attack is resolved. We propose such a mitigation scheme, QBGP, which decouples the propagation of a path and the adoption of a path for data forwarding. QBGP does not use suspicious paths to forward data traffic, but still propagates them in the routing system to facilitate attack detection. It can protect data delivery from routing announcements of false sub-prefixes, false origins, false nodes and false links. QBGP incurs overhead only when there are suspicious paths, which happen infrequently in real BGP traces. Results from large scale simulations and BGP trace analysis show that QBGP is light-weight yet effective, and it converges faster and incurs less overhead than Pretty Good BGP.

The common objective of network traffic engineering is to minimize the maximal link utilization in a network in order to accommodate more traffic and reduce the chance of congestion. Traditionally this is done by either optimizing OSPF link weights or using MPLS tunnels to direct traffic. However, they both have problems: OSPF weight optimization triggers network-wide convergence and significant traffic shift, while pure MPLS approach requires a full mesh of tunnels to be configured throughout the network. This paper formulates the traffic engineering problem as a Multi-Commodity Flow problem with hybrid MPLS/OSPF routing (MCFTE). As a result, the majority of traffic is routed by regular OSPF, while only a small number of MPLS tunnels are needed to fine-tune the traffic distribution. It keeps OSPF link weights unchanged to avoid triggering network convergence, and needs far fewer MPLS tunnels than the full-mesh to adjust traffic. Compared with existing hybrid routing approaches, MCFTE achieves the optimal link utilization, runs about two orders of magnitude faster, and is more robust against measurement inaccuracy in traffic demand.