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1、Chapter 13. Routing Choices第13章路由选择In the early days of networking, huge projects were undertaken to determine the best在早期的网络、大型项目进行确定最佳routing protocol for some definition of best. For instance, one project commissioned路由协议的一些“最好的定义。“例如，一个项目委托by the US Air Force attempted to measure the speed of co
2、nvergence for each of the由美国空军试图衡量收敛的速度primary routing protocols (OSPF, IS-IS, and EIGRP), how much bandwidth each protocol主要路由协议(OSPF是什么，EIGRP),多少带宽每个协议used under normal operation, how much bandwidth was required when the protocol was在正常的操作下，使用协议时需要多少带宽converging (given a specific network topology
3、and breakage scenarios), how many融合(给定一个特定的网络拓扑和破损的场景，有多少network engineers knew each of the protocols under investigation, and a number of other网络工程师知道每个协议接受调查，和其他一些factors. Ultimately, the project was designed to churn all these factors together and因素。最终，该项目旨在生产和所有这些因素在一起produce a single answer.产生一
4、个答案。Underlying all these calculations was always some set of assumptions assumptions基本所有这些计算总是assumptions-assumptions的些设置rarely ever brought out into the light of day and clearly examined, much less fully justified.很少了天日，明确检查，更充分的理由。These assumptions are, in reality, the interesting piece of the “wh
5、ich routing protocol ”这些假设是，在现实中，“哪个路由协议”的有趣puzzle. Here you will find the real intersection between the business and technology谜题。在这里你会发现真正的业务和技术之间的十字路口choices.选择。The first part of this chapter will deal with the “which routing protocol is best “ question, 本章的第一部分将处理”，路由协议是最女?的”问题，but we ll be conc
6、erned with exposing the questions network architects need to ask in但我们会关心揭露网络架构师需要问的问题order to answer that question, rather than providing a one size fits all solution.为了回答这个问题，而不是提供一个一刀切的解决方案。Beyond choosing a routing protocol, there are questions around best practices in除了选择路由协议，有问题的最佳实践deploying
7、routing; this is where the second part of this chapter concentrates. For instance,部署路由，这是本章的第二部分集中的地方。例如 ，how should flooding domain boundaries be set up in a link state protocol? Are there洪水域边界应如何建立链路状态协议？有trade-offs in different plans or designs?权衡不同的计划或设计吗？Finally, we ll consider a different set
8、of questions about routing protocol deployment,最后，我们将考虑一组不同的路由协议部署问题specifically related to the current “ BGP everywhere trend so common in large scale专门针对当前“边界网关协议无处不在”的趋势在大规模如此常见networks designs. Is end-to-end BGP really the best answer to resolve the routing网络设计。端到端边界网关协议是最好的答案来解决路由problems moder
9、n networks face? What problems do networks designed with end-to-end现代网络面临的问题？什么问题做网络设计的端到端BGP face?边界网关协议的脸吗？Which Routing Protocol?路由协议？What are the traditional questions surrounding the choice of a routing protocol? Most有哪些传统问题周围的一种路由协议的选择？大多数network operators will jump to two questions:网络运营商将跳转到两
10、个问题：? How fast does it converge?收敛的速度有多快？258258年? Is it proprietary?它是专有的吗？These two questions quickly become the center of virtually any discussion on choosing a这两个问题迅速成为任何讨论选择的中心routing protocol. But are they the right questions? There is another set of questions every路由协议。但他们是正确的问题吗？有另一组的每一个问题net
11、work designer should consider questions that bring the relationship between the网络设计师应该考虑质疑，带之间的关系business and technology more into view. These questions include the following:业务和技术更多的视图。这些问题包括以下几点：? Which protocol is easier to configure?协议更容易配置？? Which protocol is easier to troubleshoot?协议更容易解决？? Wh
12、ich protocol degrades in a way that provides the best support for the business works?这协议降解的方式提供了最佳的对业务工作的支持during failures?在失败？? Which protocol works best on the topology the business usually builds?协议效果最好的业务通常构建拓扑？Let s consider each of these questions in turn.让我们依次考虑这些问题。How Fast Does the Routing
13、Protocol Converge?路由协议收敛有多快？Convergence speed, although often discussed, debated, and discovered, is a rather收敛速度，虽然经常讨论、辩论和发现，是一个相当slippery concept to define. We must begin with the rather benign sounding question:难以把握的概念来定义。我们必须开始，而良性测深的问题：What does it mean for the network to be converged? When te
14、sting for convergence,是什么意思的网络聚合吗 ？为收敛测试时，engineers often set up small, simple test beds that make for easy control and工程师通常设置小，容易控制和简单的测试床measurement. They then use various methods (such as those outlined in RFC 4061,4062,测量。然后他们利用各种方法(如RFC 4061中概述，4062年，and 4063), to determine when the routing pro
15、tocol has finished calculating the best path和4063年)，以确定当路由协议已经完成了计算最佳路径to each possible destination within the (simple) network. Or the engineer might use a内的每个可能的目的地(简单的)网络。或工程师可以使用traffic generator to determine how many packets are dropped in the (simple) network流量发生器来确定有多少(简单的)网络数据包被丢弃during a convergence event.在一个收敛的事件。While all this measurement is fine, it doesn t really answer real-world questions. As a虽然所有这些测量是好的，但并没有真正回答现实问题。作为一个counterexample, let s consider the global Internet. The global Internet is made up of tens 反例，让我们考虑全球互联网。全球互联
