java400本精心收藏.juniper教学讲义

1、Organization, productEricsson AXI 520/580 Internet EngineerModule 10: 5.0 and Previous Class of Service (CoS)Module ObjectivesClass of Service (CoS) overviewDiscuss the main functions that effect preferred treatment of traffic in JUNOS softwareMonitoring ing trafficTraffic classificationOutput queui

2、ngPrecedence bit re-mappingTransmission schedulingCongestion avoidanceDiscuss COS “End-To-End” strategiesCoS OverviewCoS is the preferential treatment of packets with certain characteristicsYou define which packets get treated preferentiallyCertain applications can benefit from CoSReal-time applicat

3、ions versus non-real-time applicationsAll routers in a network must support CoS setting for applications to fully benefitIPv4 packetsIP Precedence bits in Type of Service (ToS) field can be used for CoSToS values can be mapped to CoS mechanismsMPLS packets (NOT covered in this course)EXP bits can be

4、 used for CoSMapping to IP Precedence bitsIP PrecedenceDefined in the Precedence bits of ToS field in IP header3 Precedence bits 8 possible Precedence valuesToS field has been interpreted in several different ways over time (DoD levels, DiffServ, minimize delay, etc.)VERHLENPRECToSTOTAL LENGTHIDENTI

5、FIERFLAGSFRAGMENT OFFSETTIME TO LIVEPROTOCOLCHECKSUMSOURCE IP ADDRESSDESTINATION IP ADDRESSOPTIONSPADDINGPrecedenceBits32 BITSQueue ServicingQueue servicing is how the queues are emptied with respect to each otherStrict Round Robin shares output bandwidth fairlyWeighted Round-Robin (WRR) allows queu

6、e (and therefore traffic) differentiationQueues are serviced sequentiallyWeight is based on percentage of the total available bandwidth on the output interfaceHigher-weighted queues send more packets each time they are servicedVariable queue depths also provide some measure of control preferenceImpa

7、ct on latencyJUNOS CoS ComponentsHardware monitoring of input traffic for congestionInput traffic classificationOutput queue selectionPrecedence bit rewritingServicing output queues for transmissionMonitoring output queue congestion and dropping packets (RED)Applying CoS Components “ Think End-to-En

8、d ”JUNOS CoS ComponentsCoS Hardware Flow OverviewWeightedRoundRobin T.O.S.MapInputTrafficHardwareInput L2PolicingDS3/ATMPICs OnlyLSB of PrecedenceField set?YesSetPLPNoTrafficOverThreshold?DroporTag?YesNoQueue 0Queue 1Queue 2Queue 3PrecedenceFieldRewritePassesRED DropProfilesYesNoTransmitPacketDropPa

9、cketHardware monitoring of input traffic for congestionInput traffic classificationOutput queue selectionPrecedence bit rewritingServicing output queues for transmissionMonitoring output queue congestion and dropping packets (RED)Applying CoS Components “ Think End-to-End ”JUNOS CoS ComponentsHardwa

10、re monitoring of input trafficWeightedRoundRobin T.O.S.MapInputTrafficHardwareInput L2PolicingDS3/ATMPICs OnlyLSB of PrecedenceField set?YesSetPLPNoTrafficOverThreshold?DroporTag?YesNoQueue 0Queue 1Queue 2Queue 3PrecedenceFieldRewritePassesRED DropProfilesYesNoTransmitPacketDropPacketMonitoring ing

11、TrafficToken bucket mechanism is supported on certain interfacesSONET, T1, T3, E1, E3Transmit-bucket and Receive-bucket can be definedPIC I/O Manager ASIC checks input traffic against a configured token bucket parameters and leaky bucket algorithmIf the flow exceeds the buckets threshold:Drop the pa

12、cketsTag the packets (if configured)PIC sets the PLP bit in the notification recordOther Input CoS mechanisms existATM PIC Traffic-Shaping ProfileCBR and VBR rate configurationHardware monitoring of input traffic for congestionInput traffic classificationOutput queue selectionPrecedence bit rewritin

13、gServicing output queues for transmissionMonitoring output queue congestion and dropping packets (RED)Applying CoS Components “ Think End-to-End ”JUNOS CoS ComponentsIP II Classification FeaturesWeightedRoundRobin T.O.S.MapInputTrafficHardwareInput L2PolicingDS3/ATMPICs OnlyLSB of PrecedenceField se

14、t?YesSetPLPNoTrafficOverThreshold?DroporTag?YesNoQueue 0Queue 1Queue 2Queue 3PrecedenceFieldRewritePassesRED DropProfilesYesNoTransmitPacketDropPacketFirewall Rate Policer FunctionPolicy Classification OverrideRate PolicingA filter can rate-limit specific trafficFirewall filter match conditions are

15、used to specify source/destination address, protocol, etc.Traffic that matches the filter is then policed according to an average bandwidth and a burst sizeWhen traffic exceeds the policing parameters, it can be:DiscardedHave its Packet Loss Priority (PLP) bit setQueued for transmission in a differe

16、nt output queueOverride Input Classification You can optionally override ing classification based on destination addressesThree parts involved when configuring input classification override:Define a Policy ClassAssociate Policy Class with a Routing PolicyApply the Policy to the Forwarding TableHardw

17、are monitoring of input traffic for congestionInput traffic classificationOutput queue selectionPrecedence bit rewritingServicing output queues for transmissionMonitoring output queue congestion and dropping packets (RED)Applying CoS Components “ Think End-to-End ”JUNOS CoS ComponentsIP Precedence M

18、appingWeightedRoundRobin T.O.S.MapInputTrafficHardwareInput L2PolicingDS3/ATMPICs OnlyLSB of PrecedenceField set?YesSetPLPNoTrafficOverThreshold?DroporTag?YesNoQueue 0Queue 1Queue 2Queue 3PrecedenceFieldRewritePassesRED DropProfilesYesNoTransmitPacketDropPacketMap traffic to a particular output queu

19、e based on T.O.S BitsInput Traffic ClassificationMap traffic to a particular output queueIf you do, you must assign resources to that queueIPv4 packets can be mapped to queue based on Precedence bitsInput interface ing IPv4 Precedence bits (and corresponding classification) can be overriddenMPLS pac

20、kets are placed in queue 0 by defaultMPLS packets can be statically mapped based on the three CoS (EXP) bits in the MPLS headerMPLS packets inherit IP Precedence bits by default but is still mapped into queue 0 unless furthered configuration is performedMPLS CoS configuration is not covered in this

21、courseJUNOS Queuing DefaultsPrecedence BitsIP HeaderToSPacket Loss Priority (PLP)0low probability1high probability0, 111530, 1020, 1010, 1000110950PLP BitQueue BitsDefault WRR%Queue NumberOutput QueuesEach interface has four output transmission queuesQueue 0: Low priority traffic, 95% of output inte

22、rface BWQueues 1 and 2: undefinedQueue 3: High priority traffic, 5% of output interface BWWhy these defaults?You would expect to have a small percentage of high priority traffic and a higher priority trafficIf not, you can configure something other than the defaultsIf there is no congestion, there i

23、s no hard limit (e.g., low priority traffic can go above 95%)NOTE: Routing overhead traffic is high priority by defaultEach queue can be configured with:A WRR service interval (output-queue weight)A buffer size (output-queue buffer-percentage)Classify and Map ing PacketsClassify and Map IPv4 Packets

24、 to Output Queues, based on Precedence BitsDefault Precedence bits 000 101 to Queue 0Network Control packets (110, 111) to Queue 3PLP bit is the least significant bit (LSB) of the priority bits000, 010, 100 higher priority (lower probability of drop)001, 011, 101 lower priority (higher probability o

25、f drop)After defining the mapping, associate with an Output FPC and InterfaceViewing a Precedence Map labhost show chassis CoSCoS information: FPC 0: precedence-map Default: bits 000 output-queue 0; bits 001 output-queue 0; bits 010 output-queue 0; bits 011 output-queue 0; bits 100 output-queue 0; b

26、its 101 output-queue 0; bits 110 output-queue 3; bits 111 output-queue 3; drop-profile Default: msp-profile: fill 100 drop 100 plp-set-queue-profile: fill 100 drop 100 plp-clear-queue-profile: fill 100 drop 100 Hardware monitoring of input traffic for congestionInput traffic classificationOutput que

27、ue selectionPrecedence bit rewritingServicing output queues for transmissionMonitoring output queue congestion and dropping packets (RED)Applying CoS Components “ Think End-to-End ”JUNOS CoS ComponentsCoS Output ModificationsInputTrafficWeightedRoundRobin T.O.S.MapHardwareInput L2PolicingDS3/ATMPICs

28、 OnlyLSB of PrecedenceField set?YesSetPLPNoTrafficOverThreshold?DroporTag?YesNoQueue 0Queue 1Queue 2Queue 3PrecedenceFieldRewritePassesRED DropProfilesYesNoTransmitPacketDropPacketSetting the ToS values to effect the next hopPrecedence Bit RewritingAfter packets have been received and classified, th

29、e router can rewrite the IP precedence bitsFor each output transmission queue you canSet one value for all packets headed to that queue that have the PLP set A second value for all packets whose PLP bit is not setExample application:An source outside your AS is sending packets with certain IP preced

30、ence setting that conflict with your precedence settingsYou can rewrite precedence bits to be compatible with your networks policiesHardware monitoring of input traffic for congestionInput traffic classificationOutput queue selectionPrecedence bit rewritingServicing output queues for transmissionMon

31、itoring output queue congestion and dropping packets (RED)Applying CoS Components “ Think End-to-End ”JUNOS CoS ComponentsQueue Buffering and SchedulingInputTrafficWeightedRoundRobin T.O.S.MapHardwareInput L2PolicingDS3/ATMPICs OnlyLSB of PrecedenceField set?YesSetPLPNoTrafficOverThreshold?DroporTag

32、?YesNoQueue 0Queue 1Queue 2Queue 3PrecedenceFieldRewritePassesRED DropProfilesYesNoTransmitPacketDropPacketOutput Queue Memory ManagementWeighted Round Robin Bandwidth SchedulingServicing the Output QueuesWRR algorithm is used to schedule packets for transmissionServicing alternates among the four q

33、ueues depending on the queues credit value, and determines from which queue the next packet is transmittedThe higher the weight, the more frequent the servicingPWRR ExampleTraffic headed for interfaceOutput interfaceQ0Q1Q2Q3Q0 gets 3/7 = 43% Q1 gets 2/7 = 29%Q2 gets 1/7 = 14%Q3 gets 1/7 = 14%Hardwar

34、e monitoring of input traffic for congestionInput traffic classificationOutput queue selectionPrecedence bit rewritingServicing output queues for transmissionMonitoring output queue congestion and dropping packets (RED)Applying CoS Components “ Think End-to-End ”JUNOS CoS ComponentsCongestion Manage

35、mentWeightedRoundRobin T.O.S.MapInputTrafficHardwareInput L2PolicingDS3/ATMPICs OnlyLSB of PrecedenceField set?YesSetPLPNoTrafficOverThreshold?DroporTag?YesNoQueue 0Queue 1Queue 2Queue 3PrecedenceFieldRewritePassesRED DropProfilesYesNoTransmitPacketDropPacketUse The Random Early Discard algorithm To

36、 control queue fill rates and avoid congestion problemsRandom Early DetectionRandom Early Detection (RED) is a congestion avoidance mechanismIt is proactiveRED anticipates congestion and randomly drops packets from the head of the queuePrevents the queue from filling and causing tail dropCauses TCP

37、to “behave itself” and back offAffects fewer individual TCP sessionsUDP isnt going to back off, but thats OKCongestion and Dropping PacketsRED tries to anticipate congestion and react so that the queue never actually es congestedRED proactively drops packets according to a Drop Profiles, which are b

38、ased on:Output queue fullnessDrop ProbabilitySeparate Drop Profiles are defined for:Packets whose PLP is set plp-set-profilePackets whose PLP is not set plp-clear-profileThe aggregate stream (e.g., all packet in the queue) stream-profileFor each packet, RED uses the two applicable profiles to make p

39、acket dropping decisionPackets with PLP=0 get stream-profile and plp-clear-profilePackets with PLP=1 get stream-profile and plp-set-profilePacket must “pass” both profile tests to be droppedHardware monitoring of input traffic for congestionInput traffic classificationOutput queue selectionPrecedenc

40、e bit rewritingServicing output queues for transmissionMonitoring output queue congestion and dropping packets (RED)Applying CoS Components “ Think End-to-End ”JUNOS CoS Components“ Think End-to-End ”There are many CoS mechanisms, but it is rare to use all of them simultaneouslyConsistent and delibe

41、rate application across the network is keyA well Planned Ingress, Transit, and Egress CoS strategy is required for a successful implementation !Applying CoS ComponentsSample Voice over IP End-to-End CoS StrategyApplying CoS ComponentsApplying CoS On IngressVOIPGatewayIngressTransitTransitEgressVOIPGatewayVoice over IPMixed Data TrafficIngress router COS strategyIdentify L3/L4 components of trafficIdentify default TOS bit value from L3 header.On Ingress router map traffic into