基于流的路由和openflow [英] Flow based routing and openflow
问题描述
这可能不是典型的 stackoverflow 问题.
This may not be the typical stackoverflow question.
我的一位同事一直在猜测，基于流的路由将成为网络领域的下一件大事.Openflow 提供在大型应用程序、IT 数据中心等中使用低成本交换机的技术；替换 Cisco、HP 等交换机和路由器.理论上，您可以通过简单的配置创建这些 openflow 交换机的层次结构，例如.没有生成树.开放流将仅使用交换机层次结构的知识(无路由器)将每个流路由到适当的交换机/交换机端口.该解决方案旨在为企业节省资金并简化网络.
A colleague of mine has been speculating that flow-based routing is going to be the next big thing in networking. Openflow provides the technology to use low cost switches in large application, IT data-centers, etc; replacing Cisco, HP, etc switch and routers. The theory is that you can create a hierarchy these openflow switches with simple configuration, eg. no spanning tree. Open flow will route each flow to the appropriate switch/switch-port, using only the knowledge of the hierarchy of switches (no routers). The solution is suppose to save enterprises money and simplify networking.
问.他推测这可能会极大地改变企业网络.由于许多原因，我持怀疑态度.我想听听你的想法.
Q. He is speculating that this may dramatically change enterprise networking. For many reasons, I am skeptical. I would like to hear your thoughts.
推荐答案
为了评估基于流的网络和 OpenFlow 的未来，这里是思考的方式.
In order to assess the future of flow-based networking and OpenFlow, here’s the way to think about it.
从硅趋势开始:摩尔定律(每 18-24 个月 2 倍晶体管)，以及单芯片上可用 I/O 带宽的相关但较慢的改进(大约每 30-36 个月 2 倍)).您现在可以购买具有 64 个端口的全功能 10GbE 单芯片交换机，以及具有相当总 I/O 带宽的 40GbE 和 10GbE 端口混合的芯片.
It starts with the silicon trends: Moore’s Law (2X transistors per 18-24 months), and a correlated but slower improvement in the I/O bandwidth available on a single chip (roughly 2X every 30-36 months). You can now buy full-featured 10GbE single chip switches with 64 ports, and chips which have a mix of 40GbE and 10GbE ports with comparable total I/O bandwidth.
有多种方式将它们物理连接到网格中(忽略生成树的无环路约束和以太网学习 MAC 地址的方式).在高性能计算 (HPC) 世界中，已经完成了大量工作，使用 InfiniBand 和其他协议构建集群，使用小型交换机的网格将计算服务器联网.这现在被应用于以太网网状网络.CLOS 或胖树拓扑的几何结构支持具有大量端口的两级网格.因此，数学是:其中 n 是每个芯片的端口数，您可以在两级网格中连接的设备数量为 (n*2)/2，您可以在三级网格中连接的数量舞台网格为 (n*3)/4.虽然使用标准生成树和学习，生成树协议将禁用到第二阶段的多路径链路，但大多数以太网交换机供应商都有某种多机箱链路聚合协议，可以绕过多路径限制.在这方面也有标准工作.尽管可能并不明显，但绝大多数链路聚合方案分配流量，因此任何给定流的所有帧都采用相同的路径.这样做是为了最大限度地减少乱序帧，这样它们就不会被某些更高级别的协议丢弃.他们本可以选择将此称为基于流的多路复用"，但他们却将其称为链路聚合".
There are a variety of ways physically connect these in a mesh (ignoring the loop-free constraints of spanning tree and the way Ethernet learns MAC addresses). In the high performance computing (HPC) world, a lot of work has been done building clusters with InfiniBand and other protocols using meshes of small switches to network the compute servers. This is now being applied to Ethernet meshes. The geometry of a CLOS or fat-tree topology enables a two stage mesh with a large number of ports. The math is thus: Where n is the # of ports per chip, the number of devices you can connect in a two-stage mesh is (n*2)/2, and the number you can connect in a three-stage mesh is (n*3)/4. While with standard spanning tree and learning, the spanning tree protocol will disable the multi-path links to the second stage, most of the Ethernet switch vendors have some sort of multi-chassis Link Aggregation protocol which gets around the multi-pathing limitation. There is also standards work in this area. Although it might not be obvious, the vast majority of Link Aggregation schemes allocate traffic so all the frames of any given flow take the same path. This is done in order to minimize out-of-order frames so they don’t get dropped by some higher level protocol. They could have chosen to call this "flow based multiplexing" but instead they call it "link aggregation".
总结以上几点，具有外部管理平面的以太网交换机网状网络具有多路径流量，其中流量保持有序是进化的，而不是革命性的，并且很可能成为主流.至少有一家大公司瞻博网络(Juniper)就他们对这种方法的支持发表了重要的公开声明.我将所有这些都称为基于流的路由".
Summarizing the points above, meshes of Ethernet switches with an external management plane with multipath traffic where flows are kept in order is evolutionary, not revolutionary, and is likely to become mainstream. At least one major company, Juniper, has made a big public statement about their endorsement of this approach. I'd call all of these "flow-based routing".
尽管有瞻博网络和其他供应商的专有方法，但这是一个迫切需要标准的领域.开放网络基金会 (ONF) 的成立是为了促进该领域的标准，从 OpenFlow 开始.几个月后，ONF 的 60 多名成员将庆祝成立一周年.我相信每个成员都支付了数万美元才能加入.虽然 OpenFlow 协议在被广泛采用之前还有很长的路要走，但它确实有动力.
Juniper and other vendors’ proprietary approaches notwithstanding, this is an area that cries out for standards. The Open Networking Foundation (ONF), was founded to promote standards in this area, starting with OpenFlow. Within a couple of months, the sixty+ members of ONF will be celebrating their first year anniversary. Each member has, I am led to believe, paid tens of thousands of dollars to join. While the OpenFlow protocol has a ways to go before it is widely adopted, it has real momentum.
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