
- •QoS Overview
- •“Do I Know This Already?” Quiz
- •QoS: Tuning Bandwidth, Delay, Jitter, and Loss Questions
- •Foundation Topics
- •QoS: Tuning Bandwidth, Delay, Jitter, and Loss
- •Bandwidth
- •The clock rate Command Versus the bandwidth Command
- •QoS Tools That Affect Bandwidth
- •Delay
- •Serialization Delay
- •Propagation Delay
- •Queuing Delay
- •Forwarding Delay
- •Shaping Delay
- •Network Delay
- •Delay Summary
- •QoS Tools That Affect Delay
- •Jitter
- •QoS Tools That Affect Jitter
- •Loss
- •QoS Tools That Affect Loss
- •Summary: QoS Characteristics: Bandwidth, Delay, Jitter, and Loss
- •Voice Basics
- •Voice Bandwidth Considerations
- •Voice Delay Considerations
- •Voice Jitter Considerations
- •Voice Loss Considerations
- •Video Basics
- •Video Bandwidth Considerations
- •Video Delay Considerations
- •Video Jitter Considerations
- •Video Loss Considerations
- •Comparing Voice and Video: Summary
- •IP Data Basics
- •Data Bandwidth Considerations
- •Data Delay Considerations
- •Data Jitter Considerations
- •Data Loss Considerations
- •Comparing Voice, Video, and Data: Summary
- •Foundation Summary
- •QoS Tools and Architectures
- •“Do I Know This Already?” Quiz
- •QoS Tools Questions
- •Differentiated Services Questions
- •Integrated Services Questions
- •Foundation Topics
- •Introduction to IOS QoS Tools
- •Queuing
- •Queuing Tools
- •Shaping and Policing
- •Shaping and Policing Tools
- •Congestion Avoidance
- •Congestion-Avoidance Tools
- •Call Admission Control and RSVP
- •CAC Tools
- •Management Tools
- •Summary
- •The Good-Old Common Sense QoS Model
- •GOCS Flow-Based QoS
- •GOCS Class-Based QoS
- •The Differentiated Services QoS Model
- •DiffServ Per-Hop Behaviors
- •The Class Selector PHB and DSCP Values
- •The Assured Forwarding PHB and DSCP Values
- •The Expedited Forwarding PHB and DSCP Values
- •The Integrated Services QoS Model
- •Foundation Summary
- •“Do I Know This Already?” Quiz Questions
- •CAR, PBR, and CB Marking Questions
- •Foundation Topics
- •Marking
- •IP Header QoS Fields: Precedence and DSCP
- •LAN Class of Service (CoS)
- •Other Marking Fields
- •Summary of Marking Fields
- •Class-Based Marking (CB Marking)
- •Network-Based Application Recognition (NBAR)
- •CB Marking show Commands
- •CB Marking Summary
- •Committed Access Rate (CAR)
- •CAR Marking Summary
- •Policy-Based Routing (PBR)
- •PBR Marking Summary
- •VoIP Dial Peer
- •VoIP Dial-Peer Summary
- •Foundation Summary
- •Congestion Management
- •“Do I Know This Already?” Quiz
- •Queuing Concepts Questions
- •WFQ and IP RTP Priority Questions
- •CBWFQ and LLQ Questions
- •Comparing Queuing Options Questions
- •Foundation Topics
- •Queuing Concepts
- •Output Queues, TX Rings, and TX Queues
- •Queuing on Interfaces Versus Subinterfaces and Virtual Circuits (VCs)
- •Summary of Queuing Concepts
- •Queuing Tools
- •FIFO Queuing
- •Priority Queuing
- •Custom Queuing
- •Weighted Fair Queuing (WFQ)
- •WFQ Scheduler: The Net Effect
- •WFQ Scheduling: The Process
- •WFQ Drop Policy, Number of Queues, and Queue Lengths
- •WFQ Summary
- •Class-Based WFQ (CBWFQ)
- •CBWFQ Summary
- •Low Latency Queuing (LLQ)
- •LLQ with More Than One Priority Queue
- •IP RTP Priority
- •Summary of Queuing Tool Features
- •Foundation Summary
- •Conceptual Questions
- •Priority Queuing and Custom Queuing
- •CBWFQ, LLQ, IP RTP Priority
- •Comparing Queuing Tool Options
- •“Do I Know This Already?” Quiz
- •Shaping and Policing Concepts Questions
- •Policing with CAR and CB Policer Questions
- •Shaping with FRTS, GTS, DTS, and CB Shaping
- •Foundation Topics
- •When and Where to Use Shaping and Policing
- •How Shaping Works
- •Where to Shape: Interfaces, Subinterfaces, and VCs
- •How Policing Works
- •CAR Internals
- •CB Policing Internals
- •Policing, but Not Discarding
- •Foundation Summary
- •Shaping and Policing Concepts
- •“Do I Know This Already?” Quiz
- •Congestion-Avoidance Concepts and RED Questions
- •WRED Questions
- •FRED Questions
- •Foundation Topics
- •TCP and UDP Reactions to Packet Loss
- •Tail Drop, Global Synchronization, and TCP Starvation
- •Random Early Detection (RED)
- •Weighted RED (WRED)
- •How WRED Weights Packets
- •WRED and Queuing
- •WRED Summary
- •Flow-Based WRED (FRED)
- •Foundation Summary
- •Congestion-Avoidance Concepts and Random Early Detection (RED)
- •Weighted RED (WRED)
- •Flow-Based WRED (FRED)
- •“Do I Know This Already?” Quiz
- •Compression Questions
- •Link Fragmentation and Interleave Questions
- •Foundation Topics
- •Payload and Header Compression
- •Payload Compression
- •Header Compression
- •Link Fragmentation and Interleaving
- •Multilink PPP LFI
- •Maximum Serialization Delay and Optimum Fragment Sizes
- •Frame Relay LFI Using FRF.12
- •Choosing Fragment Sizes for Frame Relay
- •Fragmentation with More Than One VC on a Single Access Link
- •FRF.11-C and FRF.12 Comparison
- •Foundation Summary
- •Compression Tools
- •LFI Tools
- •“Do I Know This Already?” Quiz
- •Foundation Topics
- •Call Admission Control Overview
- •Call Rerouting Alternatives
- •Bandwidth Engineering
- •CAC Mechanisms
- •CAC Mechanism Evaluation Criteria
- •Local Voice CAC
- •Physical DS0 Limitation
- •Max-Connections
- •Voice over Frame Relay—Voice Bandwidth
- •Trunk Conditioning
- •Local Voice Busyout
- •Measurement-Based Voice CAC
- •Service Assurance Agents
- •SAA Probes Versus Pings
- •SAA Service
- •Calculated Planning Impairment Factor
- •Advanced Voice Busyout
- •PSTN Fallback
- •SAA Probes Used for PSTN Fallback
- •IP Destination Caching
- •SAA Probe Format
- •PSTN Fallback Scalability
- •PSTN Fallback Summary
- •Resource-Based CAC
- •Resource Availability Indication
- •Gateway Calculation of Resources
- •RAI in Service Provider Networks
- •RAI in Enterprise Networks
- •RAI Operation
- •RAI Platform Support
- •Cisco CallManager Resource-Based CAC
- •Location-Based CAC Operation
- •Locations and Regions
- •Calculation of Resources
- •Automatic Alternate Routing
- •Location-Based CAC Summary
- •Gatekeeper Zone Bandwidth
- •Gatekeeper Zone Bandwidth Operation
- •Single-Zone Topology
- •Multizone Topology
- •Zone-per-Gateway Design
- •Gatekeeper in CallManager Networks
- •Zone Bandwidth Calculation
- •Gatekeeper Zone Bandwidth Summary
- •Integrated Services / Resource Reservation Protocol
- •RSVP Levels of Service
- •RSVP Operation
- •RSVP/H.323 Synchronization
- •Bandwidth per Codec
- •Subnet Bandwidth Management
- •Monitoring and Troubleshooting RSVP
- •RSVP CAC Summary
- •Foundation Summary
- •Call Admission Control Concepts
- •Local-Based CAC
- •Measurement-Based CAC
- •Resources-Based CAC
- •“Do I Know This Already?” Quiz
- •QoS Management Tools Questions
- •QoS Design Questions
- •Foundation Topics
- •QoS Management Tools
- •QoS Device Manager
- •QoS Policy Manager
- •Service Assurance Agent
- •Internetwork Performance Monitor
- •Service Management Solution
- •QoS Management Tool Summary
- •QoS Design for the Cisco QoS Exams
- •Four-Step QoS Design Process
- •Step 1: Determine Customer Priorities/QoS Policy
- •Step 2: Characterize the Network
- •Step 3: Implement the Policy
- •Step 4: Monitor the Network
- •QoS Design Guidelines for Voice and Video
- •Voice and Video: Bandwidth, Delay, Jitter, and Loss Requirements
- •Voice and Video QoS Design Recommendations
- •Foundation Summary
- •QoS Management
- •QoS Design
- •“Do I Know This Already?” Quiz
- •Foundation Topics
- •The Need for QoS on the LAN
- •Layer 2 Queues
- •Drop Thresholds
- •Trust Boundries
- •Cisco Catalyst Switch QoS Features
- •Catalyst 6500 QoS Features
- •Supervisor and Switching Engine
- •Policy Feature Card
- •Ethernet Interfaces
- •QoS Flow on the Catalyst 6500
- •Ingress Queue Scheduling
- •Layer 2 Switching Engine QoS Frame Flow
- •Layer 3 Switching Engine QoS Packet Flow
- •Egress Queue Scheduling
- •Catalyst 6500 QoS Summary
- •Cisco Catalyst 4500/4000 QoS Features
- •Supervisor Engine I and II
- •Supervisor Engine III and IV
- •Cisco Catalyst 3550 QoS Features
- •Cisco Catalyst 3524 QoS Features
- •CoS-to-Egress Queue Mapping for the Catalyst OS Switch
- •Layer-2-to-Layer 3 Mapping
- •Connecting a Catalyst OS Switch to WAN Segments
- •Displaying QoS Settings for the Catalyst OS Switch
- •Enabling QoS for the Catalyst IOS Switch
- •Enabling Priority Queuing for the Catalyst IOS Switch
- •CoS-to-Egress Queue Mapping for the Catalyst IOS Switch
- •Layer 2-to-Layer 3 Mapping
- •Connecting a Catalyst IOS Switch to Distribution Switches or WAN Segments
- •Displaying QoS Settings for the Catalyst IOS Switch
- •Foundation Summary
- •LAN QoS Concepts
- •Catalyst 6500 Series of Switches
- •Catalyst 4500/4000 Series of Switches
- •Catalyst 3550/3524 Series of Switches
- •QoS: Tuning Bandwidth, Delay, Jitter, and Loss
- •QoS Tools
- •Differentiated Services
- •Integrated Services
- •CAR, PBR, and CB Marking
- •Queuing Concepts
- •WFQ and IP RTP Priority
- •CBWFQ and LLQ
- •Comparing Queuing Options
- •Conceptual Questions
- •Priority Queuing and Custom Queuing
- •CBWFQ, LLQ, IP RTP Priority
- •Comparing Queuing Tool Options
- •Shaping and Policing Concepts
- •Policing with CAR and CB Policer
- •Shaping with FRTS, GTS, DTS, and CB Shaping
- •Shaping and Policing Concepts
- •Congestion-Avoidance Concepts and RED
- •WRED
- •FRED
- •Congestion-Avoidance Concepts and Random Early Detection (RED)
- •Weighted RED (WRED)
- •Flow-Based WRED (FRED)
- •Compression
- •Link Fragmentation and Interleave
- •Compression Tools
- •LFI Tools
- •Call Admission Control Concepts
- •Local-Based CAC
- •Measurement-Based CAC
- •Resources-Based CAC
- •QoS Management Tools
- •QoS Design
- •QoS Management
- •QoS Design
- •LAN QoS Concepts
- •Catalyst 6500 Series of Switches
- •Catalyst 4500/4000 Series of Switches
- •Catalyst 3550/3524 Series of Switches
- •Foundation Topics
- •QPPB Route Marking: Step 1
- •QPPB Per-Packet Marking: Step 2
- •QPPB: The Hidden Details
- •QPPB Summary
- •Flow-Based dWFQ
- •ToS-Based dWFQ
- •Distributed QoS Group–Based WFQ
- •Summary: dWFQ Options

778 Appendix A: Answers to the “Do I Know This Already?” Quizzes and Q&A Sections
2Describe, in general, how a queuing feature could take advantage of the work performed by a classification and marking feature.
Queuing features can perform their own classification function to place different packets into different queues. After a classification and marking tool has marked a packet, the queuing feature can look for the marked value when classifying packets.
3Which of the following QoS marking fields are carried inside an 802.1Q header: QoS, CoS, DE, ToS byte, User Priority, ToS bits, CLP, Precedence, QoS Group, DSCP, MPLS Experimental, or DS?
CoS and User Priority. CoS is the more general name, with User Priority specifically referring to the 3-bit field in the 802.1P header.
4Which of the following QoS marking fields are carried inside an IP header: QoS, CoS, DE, ToS byte, User Priority, ToS bits, CLP, Precedence, QoS Group, DSCP, MPLS Experimental, or DS?
ToS Byte, ToS bits, Precedence, DSCP, DS field.
CAR, PBR, and CB Marking
5Define the meaning of MQC, and spell out what the acronym stands for.
Modular QoS command-line interface (MQC) is a relatively new syntax structure for IOS configuration commands used in configuring several QoS features. MQC features the separation of classification logic from the actual QoS behavior (for instance, marking or queuing), and with yet another command for enabling the QoS feature on an interface. MQC is often described as a new QoS CLI, although it is really just a new set of commands.
6What configuration command lists the marking details when configuring CB marking? What configuration mode must you use to configure the command? What commands must you issue to place the configuration mode user into that mode?
The set command defines what value to mark in the frame or packet header after a packet has been classified. The command is a subcommand under the class command, which is a subcommand under the policy-map command, which in turn is a global configuration command.
7What configuration command lists the marking details when configuring CAR? What configuration mode must you use to configure the command? What commands must you issue to place the configuration mode user into that mode?
The rate-limit command defines what value to mark in the frame or packet header after a packet has been classified. The marking details are included in the same ratelimit command as the classification details. The command is a subcommand under the interface command, which is a global configuration command.

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8What configuration command lists the classification details when configuring PBR? What configuration mode must you use to configure the command? What commands must you issue to place the configuration mode user into that mode?
The match command defines the details of what must be matched to classify a packet. The command, which differs from the CB marking match command, is a subcommand under the route-map command, which is a global configuration command.
Q&A
1Describe the difference between classification and marking.
Classification processes packet headers, or possibly other information, to differentiate between multiple packets. Marking changes a field inside the frame or packet header.
2Describe, in general, how a queuing feature could take advantage of the work performed by a classification and marking feature.
Queuing features can perform their own classification function to place different packets into different queues. After a classification and marking tool has marked a packet, the queuing feature can look for the marked value when classifying packets.
3Characterize what must be true before the CoS field may be useful for marking packets.
CoS only exists in 802.1P/Q headers and ISL headers. In turn, these headers are used only on Ethernet links that use trunking. Therefore, the CoS field can only be marked or reacted to for Ethernet frames that cross an 802.1Q or ISL trunk.
4Most other QoS tools, besides classification and marking tools, also have a classification feature. Describe the advantage of classification, in terms of overall QoS design and policies, and explain why classification and marking is useful, in spite of the fact that other tools also classify the traffic.
Classification and marking, near the ingress edge of a network, can reduce the amount of work required for classification by other QoS tools. In particular, many QoS tools can classify based on marked fields without using an ACL, which reduces overhead for each QoS tool. By marking packets near the ingress edge, QoS policies can be more consistently applied. In addition, configurations for most other QoS tools become simpler, which can reduce configuration errors in the network.

780 Appendix A: Answers to the “Do I Know This Already?” Quizzes and Q&A Sections
5Which of the following classification and marking tools can classify based on the contents of an HTTP URL: class-based marking (CB marking), policy-based routing (PBR), committed access rate (CAR), network-based application recognition (NBAR), or dial peers?
NBAR actually performs the classification based on HTTP header contents. CB marking is the only tool that marks based on NBAR’s match of the URL string.
6Describe the differences between IP extended ACLs as compared with NBAR for matching TCP and UDP port numbers.
You can use both tools to match packet based on well-known port numbers. However, some higher-layer protocols allocate dynamic port numbers, making the use of extended ACLs difficult at best. NBAR can look further into the packet contents to identify what dynamic ports are currently in use by certain protocols, and match packets using those dynamic ports.
7Which of the following classification and marking tools can classify based on the outgoing interface of the route used for a packet: class-based marking (CB marking), policy-based routing (PBR), committed access rate (CAR), network-based application recognition (NBAR), or dial peers?
PBR is the only tool that can classify and mark based on route information.
8Which of the following classification and marking tools can classify based on the destination TCP port number of a packet, without using an IP ACL: class-based marking (CB marking), policy-based routing (PBR), committed access rate (CAR), network-based application recognition (NBAR), or dial peers?
None! To classify on a TCP port number, an IP ACL must be used.
9Which of the following classification and marking tools can classify based on the DSCP, without using an IP ACL: class-based marking (CB marking), policy-based routing (PBR), committed access rate (CAR), network-based application recognition (NBAR), or dial peers?
CAR, CB marking, and dial peers. Dial peers can set the DSCP value for VoIP traffic created as a result of the dial peer (as of IOS 12.2T), but that is not really classification. (Note that the DQOS exam, at time of publication of this book, covers 12.2 mainline, but not 12.2T train features.)
10Which of the following classification and marking tools can classify based on either the source or destination MAC address: class-based marking (CB marking), policy-based routing (PBR), committed access rate (CAR), network-based application recognition (NBAR), or dial peers?
CAR and CB marking. Only CB marking can examine the destination MAC.

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11Which of the following classification and marking tools can classify based on the even numbered UDP ports used for RTP traffic, with or without using an IP ACL: class-based marking (CB marking), policy-based routing (PBR), committed access rate (CAR), network-based application recognition (NBAR), or dial-peers?
CB marking. Tools that use IP ACLs can match port-number ranges, but because RTP uses only the even-numbered ports, IP ACLs cannot easily match just the evennumbered ports. Dial peers can set the DSCP value for VoIP payload (even numbered ports) created as a result of the dial peer as of IOS 12.2T, but that is not really a classification feature. It is, instead, a marking feature.
12Which of the following QoS marking fields are carried inside an 802.1Q header: QoS, CoS, DE, ToS byte, User Priority, ToS bits, CLP, Precedence, QoS Group, DSCP, MPLS Experimental, or DS?
CoS and User Priority. CoS is the more general name, with User Priority specifically referring to the 3-bit field in the 802.1P header.
13Which of the following QoS marking fields are carried inside an IP header: QoS, CoS, DE, ToS byte, User Priority, ToS bits, CLP, Precedence, QoS Group, DSCP, MPLS Experimental, or DS?
ToS byte, ToS bits, Precedence, DSCP, DS.
14Which of the following QoS marking fields are never marked inside a frame that exits a router: QoS, CoS, DE, ToS byte, User Priority, ToS bits, CLP, Precedence, QoS Group, DSCP, MPLS Experimental, or DS?
QoS Group is only used for internal purposes in GSR and 7500 series routers.
15Describe the goal of marking near the edge of a network in light of the meaning of the term “trust boundary.”
Good QoS design calls for classification and marking, based on well-defined QoS policies, as near to the ingress edge of the network as possible. However, packets marked in devices near the edge of the network may be able to be re-marked by devices whose administrators cannot be trusted. A packet can be marked by the enduser PC, for instance, but the end user can configure the value to be marked. An IP Phone, however, can mark packets, and the marked values cannot be overridden by the user of the phone. Therefore, the goal of marking near the edge must be tempered against the fact that some devices can be reconfigured for QoS by those outside the group responsible for QoS.
16Define the meaning of MQC, and spell out what the acronym stands for.
Modular QoS command-line interface (MQC) is a relatively new syntax structure for IOS configuration commands used in configuring several QoS features. MQC features the separation of classification logic from the actual QoS behavior (for

782 Appendix A: Answers to the “Do I Know This Already?” Quizzes and Q&A Sections
instance, marking or queuing), and with yet another command for enabling the QoS feature on an interface. MQC is often described as a new QoS CLI, although it is really just a new set of commands.
17What configuration command lists the classification details when configuring CB marking? What configuration mode must you use to configure the command? What commands must you issue to place the configuration mode user into that mode?
The match command defines the details of what must be matched to classify a packet. The command is a subcommand under the class-map command, which is a global configuration command.
18What configuration command lists the marking details when configuring CB marking? What configuration mode must you use to configure the command? What commands must you issue to place the configuration mode user into that mode?
The set command defines what value to mark in the frame or packet header once a packet is classified. The command is a subcommand under the class command, which is a subcommand under the policy-map command, which in turn is a global configuration command.
19What configuration command enables CB marking? What configuration mode must you use to configure the command? What commands must you issue to place the configuration mode user into that mode?
The service-policy command enables CB marking for either input or output packets on an interface. The command refers to the policy map, which in turn refers to the class maps. The command is a subcommand under the interface command, which is a global configuration command.
20What configuration command lists the classification details when configuring CAR? What configuration mode must you use to configure the command? What commands must you issue to place the configuration mode user into that mode?
The rate-limit command defines the details of what must be matched to classify a packet. The command is a subcommand under the interface command, which is a global configuration command.
21What configuration command lists the marking details when configuring CAR? What configuration mode must you use to configure the command? What commands must you issue to place the configuration mode user into that mode?
The rate-limit command defines what value to mark in the frame or packet header when a packet is classified. The marking details are included in the same rate-limit command as the classification details. The command is a subcommand under the interface command, which is a global configuration command.

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22What configuration command enables CAR? What configuration mode must you use to configure the command? What commands must you issue to place the configuration mode user into that mode?
The rate-limit command enables CAR on an interface, either for input or output packets. The command is a subcommand under the interface command, which is a global configuration command.
23What configuration command lists the classification details when configuring PBR? What configuration mode must you use to configure the command? What commands must you issue to place the configuration mode user into that mode?
The match command defines the details of what must be matched to classify a packet. The command, which his different from the CB marking match command, is a subcommand under the route-map command, which is a global configuration command.
24What configuration command lists the marking details when configuring PBR? What configuration mode must you use to configure the command? What commands must you issue to place the configuration mode user into that mode?
The set command defines what value to mark in the frame or packet header when a packet is classified. The command, which differs from the CB marking set command, is a subcommand under the route-map command, which is a global configuration command.
25What configuration command enables PBR? What configuration mode must you use to configure the command? What commands must you issue to place the configuration mode user into that mode?
The ip policy command enables PBR on an interface, always for input packets. This command refers to the route map under which the match and set commands are configured. The command is a subcommand under the interface command, which is a global configuration command.
26Describe the process dial peers use to classify and mark traffic.
At the IOS levels being referenced as of the publication of this book (IOS 12.2 mainline), dial peers can mark all VoIP packets created by the dial peer with a configured IP precedence value. As of 12.2T, dial peers can classify voice payload and voice signaling traffic using the media option and the signaling option, respectively, on the ip qos dscp command.
27What configuration command(s) lists the marking details when configuring dial peers? What configuration mode must you use to configure the command? What commands must you issue to place the configuration mode user into that mode?