QoS：基于课程的加权公平排队

思科推出了基于课程的加权公平队列（CB-WFQ）和模块化QoS CLI（MQC）在写作本博客条目[Cisco IOS 12.1（5T）]之前近8年了。检查Cisco Features Navigator以获得路由器硬件的确切版本。思科交换机不使用CB-WFQ算法。思科交换机使用加权循环（WRR），并为拥堵管理（排队）形成循环罗宾（SRR）。术语拥塞管理与CB-WFQ等不同排队技术非常紧密对齐。以下QoS技术都配置了模块化QoS CLI：•基于类的加权公平队列•基于类的标记•基于类的策略•基于类的整形•基于类的标题压缩•基于类的标题压缩•基于类的链接碎片和交错类基于用于对流量进行分类的模块化QoS CLI中的类映射分量。必须首先为路由器确定流量，以便对其进行任何有趣的事情。访问控制列表（ACL）和基于网络的应用识别（NAR）是在类地图配置模式下利用的两个最流行的分类方法。截至本写入时的常见型6500以外的任何开关平台不支持NAR。NAN不在交换机模块的ASIC（应用程序特定集成电路）中运行。 NBAR should be deployed very cautiously in the 6500 switch so the supervisor module does not become overburdened with this processing. The SUP32-PISA module supports hardware NBAR processing up to 1Gbps. The MQC allows application classes to be created by mapping application traffic to separate class-maps. Each class-map is then allocated an amount of processing time during periods of output interface congestion. The processing time is internally derived by a Cisco algorithm based on the amount of bandwidth the administrator allocated to the application class. Bandwidth can be allocated statically (8kbps increments), as a percentage of interface bandwidth, or as a percentage of remaining available bandwidth (after any static guarantees in RSVP and/or priority queue). Only one allocation mechanism can be used across all application classes of a policy or the policy will not work when the policy-map is applied to an interface. The following is an example of a simple two class-policy that allocates 10 percent of the interface bandwidth (154kbps) to FTP traffic and 20 percent of interface bandwidth 20 percent interface bandwidth (307kbps) to HTTP traffic: Class-map match-any FTP Match protocol ftp Match access-group name ftp Class-map match-any HTTP Match protocol http Match access-group name HTTP Policy-map CBWFQ Class FTP Bandwidth percent 10 Class HTTP Bandwidth percent 20 Interface Serial 0/0/0 Bandwidth 1536 service-policy output CBWFQ The names used in the class-maps are called in the policy-map CBWFQ. It is imperative that the same case be used for these names. The names used in Cisco IOS are almost always case sensitive. I can affirm that names are case sensitive in the naming of class-maps, policy-maps, named access-control lists, MPLS VPN VRFs (VPN routing and forwarding tables), and translation profiles. Since Cisco IOS is based on a Unix bash shell and Unix is case sensitive, it is safer to assume that everything in Cisco IOS is case sensitive. Notice that the bandwidth of the T-1 interface has been tuned from the default of 1.544Mbps (1544kbps) to 1536kbps. The 8kbps of framing information on a T-1 cannot be used for data transport, so we technically only have use of 1536kbps. While this may seem like the splitting of hairs, it’s concepts like this that can cost you points on a Cisco CCIE exam. In the next blog, we’ll continue this conversation to include the priority queue (PQ). CB-WFQ + PQ = LLQ (low latency queueing). More on that next time…参考文献思科特色导航www.cisco.com/go/fn