域间路由选择协议BGP-4的介绍和测试

随着因特网的发展,人们开发了许多种用于路由选择的协议,并在不断完善之中。路由选择包括决定最佳路由和由互联网传送数据包两个基本功能。路由协议选路效率的高低直接关系到互联网传送数据包的质量。根据路由选择协议应用的位置,通常分为内部网关协议（ＩＧＰ）和外部网关协议（ＥＧＰ）。内部网关协议运行于自治系统（Ａｕｔｏｎｏｍｏｕｓ Ｓｙｓｔｅｍ）边界之内;外部网关协议运行于自治系统之间。内部网关协议和外部网关协议的应用见图１。内部网关协议包括ＲＩＰ、ＯＳＰＦ、ＩＳＩＳ等;外部网关协议包括ＢＧＰ－４和已经过时的ＥＧＰ等。ＢＧＰ－４是一种用于自治系统之间路由选择的路由选择协议,并交换其他ＢＧＰ系统的路由选择和可达性信息。开发ＢＧＰ协议是为了替换它先前的协议,即已经过时的对外网关协议ＥＧＰ。 图中ＡＳ１、ＡＳ２、ＡＳ３分别代表３个不同的自治系统,３个自治系统分别运行各自的内部网关协议如ＲＩＰ、ＯＳＰＦ和ＩＳＩＳ。在三个自治系统之间运行外部网关协议如ＢＧＰ－４。一、ＢＧＰ协议的发展历程 ＢＧＰ到目前为止共有四个版本,ＢＧＰ－１、ＢＧＰ－２、ＢＧＰ－３和ＢＧＰ－４,ＢＧＰ－４是目前最高级别的版本。ＢＧＰ协议最早于１９８９年６月由Ｃｉ...     

边界网关协议——BGP4

边界网关协议是因特网上最重要的路由协议之一。它是主要用于自治系统之间交换路由信息的动态分布式路由协议。本文介绍了边界网关协议的基本原理,包括BGP的操作、BGP的路由、消息类型以及分组格式。     

边界网关协议——BGP4

边界网关协议是因特网上最重要的路由协议之一。它是主要用于自治系统之间交换路由信息的动态分布式路由协议。本介绍了边界网关协议的基本原理,包括BGP的操作、BGP的路由、消息类型以及分组格式。     

论新时期OSPF路由协议故障分析

OSPF,是一种开放式的,以最短路径优先为连接协议原则的内部网关协议.在单一自治系统的内部决策路由环境里,连接状态路由协议的实现可以运作于整个的系统内部.根据OSPF的工作机制,对于开放最短路由优先协议的支持,结合IP子网和外部路由信息的引入,可以提供很好的发送和信息接收方式.支持OSPF协议的路由器维护者描述自制系统拓扑结构的数据库,路由器往往是描述本地状态信息,在多址访问的网络过程中,网络链路状态的广播必须要使用指定的路由器传播,如果区域内路由器的连接信号发生故障,那么就可能建立不成功,无法交换信息.本文希望论述基于OSPF协议的路由链接故障产生原因,并且简述一般的解决办法.     

BGP实现网络流量负载分担

BGP是一种自治系统间的动态路由协议,广泛应用于各大电信运营商的核心IP网,它的基本功能是在自治系统间自动交换无环路的路由信息。目前,BGP不仅仅在国家网、省网中使用,许多大型城域网也使用BGP接入省网。众所周知,在自治系统网络内部,通过静态路由或者OSPF等IGP动态路由协议,只要路由器拥有等Metric的多条到达同一网段的路由,路由器就会对到达该网段的流量按照路由链路进行负载分担。在运行BGP的对等自治系统的网络中,如果边界路由器接收到多条到达同一目标网络的BGP路由,BGP最佳路径算法将会选出一条最佳路由,并仅用此路由来…     

大型IP互联网设计及路由协议(续)

4 OSPF互联网设计 OSPF是基于IP互联网协议而发展的内部网关协议(IGP)。作为IGP,OSPF在属于同一自治域(AS)的路由器间发送路由信息。一个AS是一组通过普通的路由协议交换路由信息的路由器。OSPF协议基于最短路径优先或链接状态技术。 下列两项设计工作对于成功地实现OSPF非常重要: ·区域网边缘的定义 ·地址分配     

BGP路由的属性AS_PATH分析

BGP4是为了解决复杂网络环境下的路由选择问题而设计的一种外部网关协议。随着网络的发展,它的应用也越来越广,作用也越来越突出。BGP4虽然被称为外部网关协议,但也可以用于自治系统内部,是一类双重路由选择协议。BGP4的基本机制是在采用BGP协议的两台路由器之间建立一条TCP连接,并交换消息以打开和确认BGP的连接参数,在BGP连接建立起来以后交换完全路由表。BGP全球路由表的维护依照路由触发更新机制进行,BGP路由器之间只交换必要路由更新信息。BGP有4种报文类型:Open报文用来建立连接;Update报文用来通告可达路由和撤销无效路…     

BGP协议研究及应用

BGP协议是一种用于互联网自治域系统间的动态路由协议,其主要功能是在各自治域 系统之间交换网络可达性信息。BGP协议是一种路径向量协议,使用TCP作为传送协议,保证了数据 传输的可靠性。BGP协议支持无类型的区域间路由CIDR;支持丰富的策略配置包括路由聚合、路由过 滤;支持多播路由、VPN路由,BGP协议还支持QoS等参数扩展。主要介绍了BGP协议的原理、协议软 件的工作过程及在工程中的应用。     

自治系统 可变长度子网掩码 无类别域间选路 负载平衡 策略选路

自治系统一个自治系统（AS，Au－tonomousSystem）是拥有同一选路策略、在同一技术管理部门下运行的一组路由器。自治系统可以是工作在一起以提供内部选路的内部网关协议汇集。在外部看来，整个自治系统是一个单一实体，每个自治系统有一个由互联网登记处或提供者分配给它的识别码。自治系统间的选路信息是通过外部网关协议交换的。通过把整个互联网划分成若干个自治系统，我们就能够拥有一个被分成小的、更加易于管理的网络组成的大型网络。这些小网络就被称为自治系统，自治系统可以有它们自己的一套规则和策略，能够把自己和其它自治系…     

BGP4+协议研究与应用

边界网关协议(BGP)是当前互联网上应用最广泛的外部网关协议,用于在各自治域系统之间交换网络可达性信息。BGP4+在BGP版本4的基础上进行了扩展,使之携带的路由信息既能支持IPv4也能支持IPv6。介绍了BGP4+对BGP4协议的扩展、BGP4+软件的体系结构和工作过程。通过在IPv6网络环境中的应用,验证了BGP4+软件的邻居关系建立和路由重分发等功能。目前,BGP4+软件已经在基于VxWorks的路由交换机中实现。     

Quantifying Path Exploration in the Internet

Previous measurement studies have shown the existence of path exploration and slow convergence in the global Internet routing system, and a number of protocol enhancements have been proposed to remedy the problem. However, existing measurements were conducted only over a small number of testing prefixes. There has been no systematic study to quantify the pervasiveness of Border Gateway Protocol (BGP) slow convergence in the operational Internet, nor any known effort to deploy any of the proposed solutions. In this paper, we present our measurement results that identify BGP slow convergence events across the entire global routing table. Our data shows that the severity of path exploration and slow convergence varies depending on where prefixes are originated and where the observations are made in the Internet routing hierarchy. In general, routers in tier-1 Internet service providers (ISPs) observe less path exploration, hence they experience shorter convergence delays than routers in edge ASs; prefixes originated from tier-1 ISPs also experience less path exploration than those originated from edge ASs. Furthermore, our data show that the convergence time of route fail-over events is similar to that of new route announcements and is significantly shorter than that of route failures. This observation is contrary to the widely held view from previous experiments but confirms our earlier analytical results. Our effort also led to the development of a path-preference inference method based on the path usage time, which can be used by future studies of BGP dynamics.     

Interdomain routing through QoS-class planes [Quality-of-Service-Based Routing Algorithms for Heterogeneous Networks]

This article presents an approach to delivering qualitative end-to-end quality of service (QoS) guarantees across the multiprovider Internet. We propose that bilateral agreements between a number of autonomous systems (ASs) result in the establishment of QoS-class planes that potentially extend across the global Internet. The deployment of a QoS-enhanced border gateway protocol (BGP) with different QoS-based route selection policies in each of the planes allows a range of interdomain QoS capabilities to coexist on the same network infrastructure. The article presents simulation results showing the benefits of the approach and discusses aspects of the performance of QoS-enhanced BGP     

Stable Internet routing without global coordination

The Border Gateway Protocol (BGP) allows an autonomous system (AS) to apply diverse local policies for selecting routes and propagating reachability information to other domains. However, the BGP permits ASs to have conflicting policies that can lead to routing instability. This paper proposes a set of guidelines for an AS to follow in setting its routing policies, without requiring coordination with other ASs. Our approach exploits the Internet's hierarchical structure and the commercial relationships between ASs to impose a partial order on the set of routes to each destination. The guidelines conform to conventional traffic-engineering practices of ISPs, and provide each AS with significant flexibility in selecting its local policies. Furthermore, the guidelines ensure route convergence even under changes in the topology and routing policies. Drawing on a formal model of BGP, we prove that following our proposed policy guidelines guarantees route convergence. We also describe how our methodology can be applied to new types of relationships between ASs, how to verify the hierarchical AS relationships, and how to realize our policy guidelines. Our approach has significant practical value since it preserves the ability of each AS to apply complex local policies without divulging its BGP configurations to others     

A performance evaluation of BGP‐based traffic engineering

Many Internet Service Providers tune the configuration of the Border Gateway Protocol on their routers to control their traffic. Content providers often need to control their outgoing traffic while access providers need to control their incoming traffic. We show, by means of measurements and simulations, that controlling the flow of the incoming interdomain traffic is a difficult problem. For this purpose, we first rely on detailed measurements to show the limitations of AS‐Path prepending. Then, we show by using large‐scale simulations that the difficulty of controlling the flow of the incoming traffic lies in the difficulty of predicting which BGP route will be selected by distant Autonomous Systems (ASs). Copyright © 2005 John Wiley & Sons, Ltd.     

New Framework and Mechanisms of Context‐Aware Service Composition in the Future Internet

The ongoing proliferation of new services, applications, and contents is leading the Internet to an architectural crisis owing to its inability to provide efficient solutions to new requirements. Clean‐slate architectures for the future Internet offer a new approach to tackle current and future challenges. This proposal introduces a novel clean‐slate architecture in which the TCP/IP protocol stack is decoupled in basic functionalities, that is, atomic services (ASs). A negotiation protocol, which enables context‐aware service discovery for providing adapted communications, is also specified. Then, we present how ASs can be discovered and composed according to requesters' requirements. In addition, a media service provisioning use case shows the benefits of our framework. Finally, a proof‐of‐concept implementation of the framework is described and analyzed. This paper describes the first clean‐slate architecture aligned with the work done within the ISO/IEC Future Network working group.     

Provisioning QoS in inter-domain traffic engineering

This work describes an architectural framework that allows inter-domain Traffic Engineering Label Switched Paths (TE-LSPs) with guaranteed quality of service (QoS) to be setup. Such TE-LSPs, called EQ-links, are setup by coordinating path computation elements (PCEs) of neighboring autonomous systems (ASs) along a pre-determined inter-AS path, computed through cooperative interaction between pairs of neighboring ASs. After defining the architectural requirements for the framework, we describe and analyze the Inter-AS Path Computation Protocol (IA-PCP), which computes an interdomain path at the AS level, i.e., selecting a sequence of ASs to the destination, based on a loose source routing approach. The results of the IA-PCP computations are then fed to the PCEs for complete path computation. The proposed architecture has been actually implemented within the testbed of the EuQoS project, which is aimed at enabling end-to-end QoS in the Internet. We report results related to the setup time of EQ-links, measured in the pan-European testbed of the EuQoS project, showing that path computation and setup takes an affordable time overhead.     

On inferring autonomous system relationships in the Internet

The Internet consists of rapidly increasing number of hosts interconnected by constantly evolving networks of links and routers. Interdomain routing in the Internet is coordinated by the Border Gateway Protocol (BGP). The BGP allows each autonomous system (AS) to choose its own administrative policy in selecting routes and propagating reachability information to others. These routing policies are constrained by the contractual commercial agreements between administrative domains. For example, an AS sets its policy so that it does not provide transit services between its providers. Such policies imply that AS relationships are an important aspect of the Internet structure. We propose an augmented AS graph representation that classifies AS relationships into customer-provider, peering, and sibling relationships. We classify the types of routes that can appear in BGP routing tables based on the relationships between the ASs in the path and present heuristic algorithms that infer AS relationships from BGP routing tables. The algorithms are tested on publicly available BGP routing tables. We verify our inference results with AT&T internal information on its relationship with neighboring ASs. As much as 99.1% of our inference results are confirmed by the AT&T internal information. We also verify our inferred sibling relationships with the information acquired from the WHOIS lookup service. More than half of our inferred sibling-to-sibling relationships are confirmed by the WHOIS lookup service. To the best of our knowledge, there has been no publicly available information about AS relationships and this is the first attempt in understanding and inferring AS relationships in the Internet. We show evidence that some routing table entries stem from router misconfigurations     

Some Universal Constructions of Autonomic Systems

Self-* is widely considered as a foundation for autonomic computing. The notion of autonomic systems (ASs) and self-* serves as a basis on which to build our intuition about category of ASs in general. In this paper we will specify ASs and self-* and then move on to consider some universal constructions such as products, coproducts, finite limits and colimits of ASs. All of this material is taken as an investigation of our category, the category of ASs, which we call AS.     

Inbound traffic engineering for multihomed ASs using AS path prepending

This article considers the AS path prepending approach to engineer inbound traffic for multihomed ASs. The AS path prepending approach artificially inflates the length of the AS path attribute on one of the links in hopes of diverting some of the traffic to other links. Unlike the current practice that determines the prepending length in a trial-and-error way, we propose AutoPrepend, a systematic and automated procedure for conducting prepending. The entire process consists of four components: passive measurement, active measurement, traffic change prediction, and AS path update. The main idea is to predict the traffic change due to a new prepending value before effecting the change. We have also employed a number of mechanisms to minimize intrusion into the normal operation of the Internet. We have deployed AutoPrepend on a noncommercial site and evaluated its effectiveness based on the measurements collected over six months.     

Redundancy,diversity, and connectivity to achieve multilevel network resilience,survivability, and disruption tolerance invited paper

Communication networks are constructed as a multilevel stack of infrastructure, protocols, and mechanisms: links and nodes, topology, routing paths, interconnected realms (ASs), end-to-end transport, and application interaction. The resilience of each one of these levels provides a foundation for the next level to achieve an overall goal of a resilient, survivable, disruption-tolerant, and dependable Future Internet. This paper concentrates on three critical resilience disciplines and the corresponding mechanisms to achieve multilevel resilience: redundancy for fault tolerance, diversity for survivability, and connectivity for disruption tolerance. Cross-layering and the mechanisms at each level are described, including richly connected topologies, multipath diverse routing, and disruption-tolerant end-to-end transport.