Intra-domain routing convergence with centralized control

The decentralized control scheme for routing in current IP networks has been questioned, and a centralized routing scheme has been proposed as an alternative. In this paper, we compare the convergence of centralized control scheme with decentralized link-state routing protocols. We first review the architectural advantages and challenges of centralized control. Thereafter, we identify and discuss the components of the convergence time in both schemes. We present how to achieve fast routing convergence in networks with centralized control. In particular, we analyze how to distribute forwarding information efficiently. Finally, we perform simulation studies on the convergence time for both real and synthetic network topologies and study the impact of control element location, link weights, and number of failures on the convergence time. The results show that the centralized control scheme can provide faster routing convergence than link-state routing protocols.     

BA-BGP:一种基于备份AS通告的域间路由协议

BGP协议通过触发全局、反应式收敛应对网络拓扑和策略变化,然而由于其收敛时间过长、收敛过程中大量AS经历不可达、环路,造成大量转发中断,难以支持VoIP、远程医疗等关键业务的应用。本文提出了一种基于备份AS通告的新型域间路由协议BA-BGP,在不影响BGP协议动态性的基础上,通过在更新报文中增加备份AS属性,使AS节点可以获取到达目标的备份AS地址,当节点面临瞬时失效时可将报文封装转发到与备份AS关联的路径,从而降低了转发中断。大量模拟实验证明,通过采用具有互联网特征的拓扑以及广泛采用的BGP策略,BA-BGP有效降低了链路失效引起的瞬时失效率与转发中断时间,增强了网络可靠性。     

FIR: An efficient routing strategy for tori and meshes

Recent massively parallel computers are based on clusters of PCs. These machines use one of the recently proposed standard interconnects. These interconnects either use source routing or distributed routing based on forwarding tables. While source routers are simpler, distributed routers provides more flexibility allowing the network to achieve a higher performance. Distributed routing can be implemented by a fixed hardware specific to a routing function on a given topology or by using forwarding tables. The main problem of this approach is the lack of scalability of forwarding tables. In this paper, we propose a distributed routing strategy for commercial switches, flexible interval routing, that is scalable, both in memory and routing time because it is not based on tables. At the same time, the strategy is easy to reconfigure, being able to implement the most commonly used routing algorithms in the most widely used regular topologies.     

Learning the valid incoming direction of IP packets

Packet forwarding on the Internet is solely based on the destination address of packets, and it is easy to forge the source address of IP packets without affecting the delivery of the packets. To solve this problem, one can have routers check whether or not every packet comes from a correct direction based on its source address field. However, due to routing asymmetry in today’s Internet, a router cannot simply reverse its forwarding table to determine the correct incoming direction of a packet.In this paper, we present the source address validity enforcement protocol, SAVE, which allows routers to learn valid incoming directions for any given source address. SAVE is independent from—and can work with—any specific routing protocol. By only interfacing with the forwarding table at routers, SAVE allows routers to properly propagate valid source address information from source address spaces to all destinations, and allows each router en route to build and maintain an incoming tree to associate each source address prefix with a corresponding incoming interface. The incoming tree is further valuable in handling routing changes: although a routing change at one router could affect the incoming direction of source address spaces from many locations, only the router that sees the change needs to send out new updates. Finally, SAVE has a good performance with low overhead.     

主动层次多目通信路由模型

许多应用需要IP多目通信.在Internet大规模应用IP Multicast时,有效的路由是关键.这样的多目路由协议必须是有效的、可伸缩的和增量可配置的.但是传统的Internet路由对性能是不敏感的,不能平衡负载和处理拥塞.现有的大多数多目通信路由协议不仅负责数据转发,还负责路由树的构造,这给路由器带来了极大的复杂性,而且协议的配置是手动的、费时费钱的工作.该文提出一个主动层次式Multicast路由的体系结构,采用主动网络技术将多目通信路由协议的数据转发和控制机制分开,根据链路的状态信息用主动报文控     

Experimental validation of resilient tree-based greedy geometric routing

Geometric routing is an alternative for IP routing based on longest prefix matching. Using this routing paradigm, every node in the network is assigned a coordinate and packets are forwarded towards their intended destination following a distance-decreasing policy (greedy forwarding). This approach makes the routers significantly more memory-efficient compared to the current IP routers. In this routing, greedy embeddings are used to guarantee a 100% successful delivery to every destination in the network. Most of the existing proposals lack resiliency mechanisms to react efficiently to network changes. We propose a distributed algorithm to calculate a greedy embedding based on a spanning tree of the network. In this algorithm, nodes are triggered to re-calculate their coordinates upon a change in the topology such as link or node failures. The advantage of this approach is that it recovers from topology failures within a very short period of time. We further extend the algorithm to generate backups to apply protection in distributed setups. Different trade-offs and trends of re-convergence for geometric routing have been evaluated in an emulation environment. Realistic results are achieved through emulation as no model or abstraction is involved. The proposed routing scheme is implemented in Quagga routing software and new elements are developed in Click modular router to enable greedy forwarding. For the first time, the performance of this scheme is evaluated through emulation on a large topology of 1000 nodes and the results are compared with BGP. The experimental results indicate that the proposed scheme has interesting characteristics in terms of convergence time upon a change in the network topology.     

基于SD-Torus网络的分布式IP地址查找

针对IP路由器的FIB(Forwarding Information Base)极限问题和分布式IP地址查找中的通信延迟问题,提出了SD-Torus(Semi-Diagonal Torus)直连网络。按照"临近存储"的原则,将路由表划分后存储在每个节点及其邻居节点上,以减少分布式IP地址查找中的通信延迟,提高整体的查找性能。在分析SD-Torus网络拓扑性质的基础上,提出了一种负载均衡的路由算法。基于SystemC的仿真结果表明,使用该结构可以大大降低分布式IP地址查找的通信延迟,提高系统的扩展性。该研究结果可以应用于高性能的分布式IP地址查找。     

TROP: A Novel Approximate Link-State Dissemination Framework For Dynamic Survivable Routing in MPLS Networks

In this paper, a novel approximate link-state dissemination framework, called TROP, is proposed for shared backup path protection (SBPP) in multiprotocol label switching (MPLS) networks. While performing dynamic explicit survivable routing in a distributed environment, link-state dissemination may cause a nontrivial signaling overhead in the process of exploring spare resource sharing among individual backup label switched paths (LSPs). Several previously reported studies have tackled this problem by initiating a compromise between the amount of dissemination and the achievable extent of resource sharing. The paper first summarizes the previously reported schemes into a compact and general link-state dissemination framework by way of singular value decomposition (SVD). To improve the accuracy of the matrix reconstruction and to eliminate the overestimation of the sharable spare capacity along each link, a novel SVD approach based on the min-plus algebra (also called tropical semirings) is introduced. Simulation results show that the proposed schemes can achieve a lower blocking probability than that by all the other counterpart schemes while taking the same complexity of link-state dissemination. This great advantage is gained at the expense of a longer computation time for solving a linear program (LP) in each dissemination cycle at the core nodes. We also consider the stale link-state phenomena that may cause imprecision in the routing information at the ingress nodes due to the delay in the periodic/event-driven link-state update message advertisement.     

基于SDN与NDN的卫星网络多约束路由算法

针对NDN卫星网络内容传输时延高、丢包率高且请求命中率低的问题,提出了一种基于SDN与NDN的卫星网络多约束路由算法,并命名为SNMcRA。基于SDN的集中控制与全局视图,通过建立多约束路由模型,将链路多约束信息与蚁群算法相结合以求解满足时延、带宽、丢包率多约束的代价最小路径,由节点在包转发的过程中动态完成转发表FIB和待定请求表PIT的构建。实验结果表明,该算法与DSP算法相比时延降低了35%,带宽利用率提升了29%,丢包率降低了17%,并且在请求命中率方面也具有显著优势。     

TCAM architecture for IP lookup using prefix properties

In modern IP routers, Internet protocol (IP) lookup forms a bottleneck in packet forwarding because the lookup speed cannot catch up with the increase in link bandwidth. Ternary content-addressable memories (TCAMs) have emerged as viable devices for designing high-throughput forwarding engines on routers. Called ternary because they store don't-care states in addition to 0s and 1s, TCAMs search the data (IP address) in a single clock cycle. Because of this property, TCAMs are particularly attractive for packet forwarding and classifications. Despite these advantages, large TCAM arrays have high power consumption and lack scalable design schemes, which limit their use. We propose a two-level pipelined architecture that reduces power consumption through memory compaction and the selective enablement of only a portion of the TCAM array. We also introduce the idea of prefix aggregation and prefix expansion to reduce the number of routing-table entries in TCAMs for IP lookup. We also discuss an efficient incremental update scheme for the routing of prefixes and provide empirical equations for estimating memory requirements and proportional power consumption for the proposed architecture.     

二维转发表的分解存储模型

现有互联网基于目的IP地址实施报文转发,传输过程没有关注源IP地址,转发策略不够灵活.基于目的IP地址与源IP地址的二维路由,支持网络提供更灵活的转发服务.但是,源IP地址的引入会急剧增加转发表（forward information base,简称FIB)的存储空间,大幅增加硬件成本.提出了一种二维转发表分解存储模型（decomposition storage model of two-dimensional FIB,简称DSTF),基于目的IP前缀对转发表进行分解存储.它把归属于同一个簇头IP前缀（cluster-head IP prefix,简称CP)的二维转发项集合作为一个子二维块（sub two-dimensional block,简称STB),并根据STB所属CP的不同,将转发项存储到不同的线卡（line card,简称LC).报文转发时,系统可根据CP与LC间的对应关系,快速定位报文的宿主线卡（LC_host),并在宿主线卡中实施转发处理.实验结果表明,该模型能将二维转发表均衡存储在不同线卡上,有效地减少了二维转发表在路由系统中的存储空间.     

互联网无中断转发的生存性路由协议

互联网逐渐成为通信基础设施并承载了更多的关键业务流量,即使瞬时中断也会对某些应用造成巨大损失.然而,传统路由协议在出现链路/节点故障等拓扑变化时存在收敛时间长、瞬时不可达以及环路的问题.实际测量发现,路由瞬时失效相当普遍.因此,研究人员提出多种能够保证流量无中断转发和快速恢复的路由协议.在分析瞬时失效现象以后,提出了生存性路由协议的分类方法,重点对一些重要的路由协议的核心路由机制进行深入分析,并比较其特点、性能、开销等.最后,结合该领域研究现状以及存在的问题,指出未来生存性路由的研究重点.     

MPFS: A truly scalable router architecture for next generation Internet

A new generation architecture of IP routers called massive parallel forwarding and switching （MPFS） is proposed, which is totally different from modern routers. The basic idea of MPFS is mapping complicated forwarding process into multilevel scalable switch fabric so as to implement packet forwarding in a pipelining and distributed way. This processing mechanism is named forwarding in switching （FIS）. By interconnecting multi-stage, lower speed components, called forwarding and switching nodes （FSN）, MPFS achieves better scalability in forwarding and switching performance just like MPP. We put emphasis upon IPv6 lookup problem in MPFS and propose a method for partitioning IPv6 FIB and mapping them to switch fabric. Simulation and computation results suggest that MPFS routers can support line-speed forwarding with a million of IPv6 prefixes at 40 Gbps. We also propose an implementation of 160 Tbps core router based on MPFS architecture at last.     

一种改进的Chord网络模型

经典的Chord模型中为维护Chord环路由信息而周期性执行的Stabilize操作产生了大量的消息转发。提出一种改进的Chord模型,通过使用优化的双向Finger表,使得只在节点加入或离开时才进行路由更新,降低了消息转发的开销,同时优化了路由定位算法。     

A measurement study of persistent forwarding loops on the Internet

In this paper, we present a measurement study of persistent forwarding loops and a flooding attack that exploits persistent forwarding loops. Persistent forwarding loops may share one or more links with forwarding paths to some hosts. An attacker can exploit persistent forwarding loops to overload the shared links and disrupt Internet connectivity to those hosts.To understand the extent of this vulnerability, we perform extensive measurements to systematically study persistent forwarding loops. We find that persistent forwarding loops do exist in the Internet. At least 35 million addresses experience persistent forwarding loops, and at least 11 million addresses can be attacked by exploiting such persistent forwarding loops. In addition, 87.4% of persistent forwarding loops involve routers in destination domains, which can be observed from various locations. This makes it possible to launch attacks from multiple vantage points. We also find that most persistent forwarding loops are just two hops long, which enables an attacker to significantly amplify traffic to them.We further investigate the possible cause of persistent forwarding loops, and find that about 50% of them are caused by neglecting to configure pull-up routes. We show that even if the misconfiguration occurs in a stub network, it may cause persistent forwarding loops involving routers in large ISPs, and can potentially be exploited by attackers to flood links in a backbone network. To the best of our knowledge, this is the first study of exploiting routing misconfigurations to launch DDoS attacks and understanding the impact of such attacks.     

互联网无中断转发的生存性路由协议

互联网逐渐成为通信基础设施并承载了更多的关键业务流量,即使瞬时中断也会对某些应用造成巨大损失.然而,传统路由协议在出现链路/节点故障等拓扑变化时存在收敛时间长、瞬时不可达以及环路的问题.实际测量发现,路由瞬时失效相当普遍.因此,研究人员提出多种能够保证流量无中断转发和快速恢复的路由协议.在分析瞬时失效现象以后,提出了生存性路由协议的分类方法,重点对一些重要的路由协议的核心路由机制进行深入分析,并比较其特点、性能、开销等.最后,结合该领域研究现状以及存在的问题,指出未来生存性路由的研究重点.     

Routing table partitioning for speedy packet lookups in scalable routers

Most of the high-performance routers available commercially these days equip each of their line cards (LCs) with a forwarding engine (FE) to perform table lookups locally. This work introduces and evaluates a technique for speedy packet lookups, called SPAL, in such routers. The BGP routing table under SPAL is fragmented into subsets which constitute forwarding tables for different FEs so that the number of table entries in each FE drops as the router grows. This reduction in the forwarding table size drastically lowers the amount of SRAM (e.g., L3 data cache) required in each LC to hold the trie constructed according to the prefix matching algorithm. SPAL calls for caching the lookup result of a given IP address at its home LC (denoted by LC/sub ho/, using the LR-cache), such that the result can satisfy the lookup requests for the same address from not only LC/sub ho/, but also other LCs quickly. Our trace-driven simulation reveals that SPAL leads to improved mean lookup performance by a factor of at least 2.5 (or 4.3) for a router with three (or 16) LCs, if the LR-cache contains 4K blocks. SPAL achieves this significant improvement, while greatly lowering the SRAM (i.e., the L3 data cache plus the LR-cache combined) requirement in each LC and possibly shortening the worst-case lookup time (thanks to fewer memory accesses during longest-prefix matching search) when compared with a current router without partitioning the routing table. It promises good scalability (with respect to routing table growth) and exhibits a small mean lookup time per packet. With its ability to speed up packet lookup performance while lowering overall SRAM substantially, SPAL is ideally applicable to the new generation of scalable high-performance routers.     

Performance Analysis and Route Optimization: Redistribution between EIGRP,OSPF & BGP Routing Protocols

Routing is the process of data path selection of IP networks. Routers perform path selection on the basis of routing tables stored in their memory. Routing table contains IP routes for route transformation via the best path in the networks. Service providers use different routing protocols in their enterprise networks. These routing-protocols have the limitation of non-convergence in the networks. Route redistribution is the technique which overcomes this limitation. Due to this technique, service providers can get optimized communication with IP networks where multiple routing protocols are being used. This research article focuses on the performance and redistribution of different routing protocols in medium or enterprise IP networks. A simulated network model is established in GNS3 simulator. Five Cisco-7200 series routers and a switch is used in this simulated topology. All these routers are directly connected with each other via serial links. Routing protocols EIGRP, OSPF and BGP are used in this topology and then configured route redistribution on these routers. Different types of data traffic are generated and passed through the network in order to analyze network convergence, throughput and packet delay by the use of software wire shark network analyzer and debug command. EIGRP is better in convergence and through put whereas OSPF is better in packet delay.     

Link-state routing without broadcast storming for multichannel mesh networks

A link-state routing protocol tailored for multichannel mesh networks is proposed. One drawback of using multichannel communications is the high overhead involved in broadcast operations: a transmitter should transmit a broadcast packet to all channels that may be occupied by receivers. This makes certain broadcast-intensive mechanisms, such as link-state routing, difficult to implement. The link-state routing protocol proposed in this paper is tailored for multichannel mesh networks by minimizing the broadcast overheads. This is achieved by a special set of nodes, called cluster-heads. We have implemented our protocol on a multichannel mesh network test bed and compared its performance with an AODV-like reactive routing protocol, also tailored for multichannel mesh networks. The measurements show that the proposed link-state routing protocol provides transient communications with comparable or better performance. Ways to improve the performance of the proposed routing with infrastructure access is also discussed.     

Edge-limited scalable QoS flow set-up

Although the Differentiated Services architecture supports scalable packet forwarding based on aggregate flows, the detailed procedure of Quality of Service (QoS) flow set-up within this architecture has not been well established. In this paper we explore the possibility of a scalable QoS flow set-up using a sink-tree paradigm. The paradigm initially constructs a sink tree at each egress edge router using network topology and bandwidth information provided by a QoS extended version of Open Shortest Path First (OSPF), which is a widely used link-state routing protocol. Our sink-tree paradigm dynamically reallocates network bandwidths online according to traffic demands. As a consequence, our paradigm easily supports QoS routing, resource allocation, and admission control at ingress edge routers without consulting core routers in a way that the QoS flow set-up time and overhead are minimized. Simulation results are very encouraging in that the proposed methodology requires significantly less communication overhead in setting up QoS flows compared to the traditional per-flow signaling-based methodology while still maintaining high resource utilization.