Wide Area Networks © 2000, Cisco Systems, Inc Copyright © 2000, Cisco Systems, Inc Section I Policy / Shaping Keep All Graphics Inside This Box © 2000, Cisco Systems, Inc Copyright © 2000, Cisco Systems, Inc www.cisco.com econ_0481_09_010.ppt Objectives Upon completion of this module section, you will be able to perform the following tasks: • Describe the difference between policing and shaping and how each one relates to QoS • Describe committed access rate (CAR), when to apply CAR, how to configure CAR • Describe Modular Quality of Service Command Line Interface (MQC) policing and how to configure it • Identify the three types of traffic shaping, their differences, and how to apply each Keep All Graphics Inside This Box © 2000, Cisco Systems, Inc www.cisco.com econ_0481_09_010.ppt The purpose of the lesson is to quickly survey the new policing and traffic shaping features in Cisco IOS Release 12.1, and to describe the problems they solve Copyright © 2000, Cisco Systems, Inc Customer Problems to Solve Result: Buffering = Delay or Dropped Packets 128kbps 256kbps Remote Sites 512kbps T1 Frame Relay, ATM 768kbps Central Site T1 • Central to Remote Site Speed Mismatch • Remote to Central Site Over-subscription • Control use of shared LAN, WAN, MAN media – Multi-Dwelling Unit (MDU) Keep All Graphics Inside This Box © 2000, Cisco Systems, Inc www.cisco.com econ_0481_09_010.ppt The slide shows a Frame Relay or ATM network Pay close attention to the speeds of the access lines to the remote sites on the left Suppose each site has a Committed Information Rate (CIR) close to the access speed with bursting up to the access bandwidth • What happens at the central site if the bottom two sites burst at the same time? • What happens at the central site if a server rapidly transmits data for the top left remote site? • What happens if the bottom two left sites try to send a large amount of data to the top left site? In this section, some of the QoS techniques that help resolves issues such as theseare examined Copyright © 2000, Cisco Systems, Inc Policing and Shaping Network Management Internet Policing and traffic shaping occur within the network to provide congestion management and control bursts Keep All Graphics Inside This Box © 2000, Cisco Systems, Inc www.cisco.com econ_0481_09_010.ppt In this module section, policing and traffic shaping are discussed Both of these traffic engineering methods occur within the network as indicated by the heavy ellipse in the slide They use the already marked Type of Service (ToS) or Differentiated Services Code Point (DSCP) bits discussed in the previous module With policing the rate at which traffic can flow is capped This is usually done inbound to control how fast someone sends data With shaping, smooth out bursts for a steadier flow of data Reduced burstiness helps reduce congestion in a network core Copyright © 2000, Cisco Systems, Inc Policing Policing is the QoS component that limits traffic flow to a configured bit rate: • With limited bursting capability • But no buffers, packets above the specified burst rate are dropped or have their precedence altered Keep All Graphics Inside This Box © 2000, Cisco Systems, Inc www.cisco.com econ_0481_09_010.ppt A policer typically drops traffic For example, CARs rate-limiting policer will either drop the packet or rewrite its IP Precedence, resetting the packet header's ToS bits Policing is also available through the MQC Copyright © 2000, Cisco Systems, Inc Shaping Shaping is the QoS feature component that regulates traffic flow to an average or peak bit rate: • With bursting capability • With buffers, packets that cannot be sent are queued Keep All Graphics Inside This Box © 2000, Cisco Systems, Inc www.cisco.com econ_0481_09_010.ppt A shaper typically delays excess traffic using a buffer, or queuing mechanism, to hold packets and shape the flow when the data rate of the source is higher than expected For example, Generic Traffic Shaping (GTS) uses a weighted fair queue to delay packets in order to shape the flow Depending on how it is configured, Frame Relay Traffic Shaping (FRTS) uses either a Priority Queue (PQ), a Custom Queue (CQ), or a first- in, first-out (FIFO) queue for the same sort of purpose Copyright © 2000, Cisco Systems, Inc Policing Traffic Rate Policer Traffic Traffic Traffic Policing Versus Shaping Time Shaping Traffic Traffic Time Traffic Rate Causes TCP resends Oscillation of TCP windows Policer can be marker also (CAR) Policer on input interface only Traffic Rate Traffic Rate Shaper Can adapt to network congestion (FR BECN, FECN) Time Time Keep All Graphics Inside This Box © 2000, Cisco Systems, Inc www.cisco.com econ_0481_09_010.ppt This diagram shows the effects of traffic shaping Both policing and shaping ensure that traffic does not exceed a (contracted) bandwidth limit Policing and Shaping both limit bandwidth but with different traffic impact: • Policing drops more often, more resends • Shaping adds variable delay Traffic shaping smoothes traffic by storing traffic above the configured rate in a queue When a packet arrives at the interface for transmission, the following happens: • If the queue is empty, the arriving packet is processed by the traffic shaper: – If possible, the traffic shaper sends the packet – Otherwise, the packet is placed in the queue • If the queue is not empty, the packet is placed in the queue When there are packets in the queue, the traffic shaper removes the number of packets it can send from the queue every time interval Additional details on policing and shaping can be found at: http://www.cisco.com/univercd/cc/td/doc/product/software/ios120/12cgcr/qos_c/qcpart4/qc polts.htm Copyright © 2000, Cisco Systems, Inc Topics Policing • CAR • MQC Traffic shaping Keep All Graphics Inside This Box © 2000, Cisco Systems, Inc Copyright © 2000, Cisco Systems, Inc www.cisco.com econ_0481_09_010.ppt Committed Access Rate (CAR) CAR performs three functions: • Packet classification • Packet marking—IP Precedence and QoS group setting • Manage access bandwidth through rate limiting (policing) Keep All Graphics Inside This Box © 2000, Cisco Systems, Inc www.cisco.com econ_0481_09_010.ppt CARs rate- limiting feature manages a network's access bandwidth policy by ensuring that traffic falling within specified rate parameters is sent, while dropping packets that exceed the acceptable amount of traffic or sending them with a different priority CARs exceed action is to drop packets The rate- limiting function of CAR does the following: • Allows the control the maximum rate of traffic transmitted or received on an interface • Gives the ability to define Layer aggregate or granular incoming or outgoing (ingress or egress) bandwidth rate limits and to specify traffic-handling policies when the traffic either conforms to or exceeds the specified rate limits • Uses aggregate bandwidth rate limits to match all of the packets on an interface or sub- interface • Uses granular bandwidth rate limits to match a particular type of traffic based on precedence, MAC address, or other parameters CAR is often configured on interfaces at the edge of a network to limit traffic into or out of the network VIP-distributed CAR is a version of CAR that runs on the Versatile Interface Processor (VIP) It is supported on the Cisco 7500 routers with a VIP2-40 or greater interface processor Distributed Cisco Express Forwarding (dCEF) switching must be enabled on any interface that uses VIP-Distributed CAR, even when only output CAR is configured Copyright © 2000, Cisco Systems, Inc 10 ... Additional details on policing and shaping can be found at: http://www.cisco.com/univercd/cc/td /doc/ product/software/ios120/12cgcr/qos_c/qcpart4/qc polts.htm Copyright © 2000, Cisco Systems, Inc... (slower) See the following URL for additional information: http://www.cisco.com/univercd/cc/td /doc/ product/software/ios120/12cgcr/qos_c/qcpart 1/qccar.htm Copyright © 2000, Cisco Systems, Inc... than, the CAR action options For additional information see: http://www.cisco.com/univercd/cc/td /doc/ product/aggr/10000/10ksw/qosos.htm#4 7183 Copyright © 2000, Cisco Systems, Inc 14 MQC Policing