CCIE Routing and Switching v5.0 Official Cert Guide: Classification and Marking
Blueprint topics covered in this chapter:
This chapter covers the following subtopics from the Cisco CCIE Routing and Switching written exam blueprint. Refer to the full blueprint in Table I-1 in the Introduction for more details on the topics covered in each chapter and their context within the blueprint.
- Modular QoS CLI (MQC)
- Network-Based Application Recognition (NBAR)
- QoS Classification
- QoS Marking
- Cisco AutoQoS
The goal of classification and marking tools is to simplify the classification process of other quality of service (QoS) tools by performing complicated classification steps as few times as possible. For example, a classification and marking tool might examine the source IP address of packets, incoming Class of Service (CoS) settings, and possibly TCP or UDP port numbers. Packets matching all those fields might have their IP Precedence (IPP) or DiffServ Code Points (DSCP) field marked with a particular value. Later, other QoS tools—on the same router/switch or a different one—can simply look for the marked field when making a QoS decision, rather than having to perform the detailed classification again before taking the desired QoS action.
“Do I Know This Already?” Quiz
Table 3-1 outlines the major headings in this chapter and the corresponding “Do I Know This Already?” quiz questions.
Table 3-1 “Do I Know This Already?” Foundation Topics Section-to-Question Mapping
Foundation Topics Section
Questions Covered in This Section Score
Fields That Can Be Marked for QoS Purposes
Cisco Modular QoS CLI
Classification and Marking Tools
To best use this pre-chapter assessment, remember to score yourself strictly. You can find the answers in Appendix A, “Answers to the ‘Do I Know This Already?’ Quizzes.”
According to the DiffServ RFCs, which PHB defines a set of three DSCPs in each service class, with different drop characteristics for each of the three DSCP values?
- Expedited Forwarding
- Class Selector
- Assured Forwarding
Which of the following are true about the location of DSCP in the IP header?
- High-order 6 bits of ToS byte/DS field.
- Low-order 6 bits of ToS byte.
- Middle 6 bits of ToS byte.
- Its first 3 bits overlap with IP Precedence.
- Its last 3 bits overlap with IP Precedence
Imagine that a packet is marked with DSCP CS3. Later, a QoS tool classifies the packet. Which of the following classification criteria would match the packet, assuming that the marking had not been changed from the original CS3 marking?
- Match on DSCP CS3
- Match on precedence 3
- Match on DSCP AF32
- Match on DSCP AF31
- Match on DSCP decimal 24
Imagine that a packet is marked with AF31. Later, a QoS tool classifies the packet. Which of the following classification criteria would match the packet, assuming that the marking had not been changed from the original AF31 marking?
- Match on DSCP CS3
- Match on precedence 3
- Match on DSCP 24
- Match on DSCP 26
- Match on DSCP 28
Examine the following output from a router that shows a user adding configuration to a router. Which of the following statements is true about the configuration?
Router(config)# class-map fred Router(config-cmap)# match dscp EF Router(config-cmap)# match access-group 101
- Packets that match both DSCP EF and ACL 101 will match the class.
- Packets that match either DSCP EF or ACL 101 will match the class.
- Packets that match ACL 101 will match the class, because the second match command replaces the first.
- Packets will only match DSCP EF because the first match exits the class map.
Router R1 is configured with the following three class maps. Which class map(s) would match an incoming frame whose CoS field is set to 3, IP Precedence is set to 2, and DSCP is set to AF21?
class-map match-all c1 match cos 3 4 class-map match-any c2 match cos 2 3 match cos 1 class-map match-all c3 match cos 3 4 match cos 2
- All of these answers are correct.
Examine the following example of commands typed in configuration mode to create a class map. Assuming that the class fred command was used inside a policy map, and the policy map was enabled on an interface, which of the following would be true with regard to packets classified by the class map?
Router(config)# class-map fred Router(config-cmap)# match ip dscp ef Router(config-cmap)# match ip dscp af31
- Match packets with both DSCP EF and AF31
- Match packets with either DSCP EF or AF31
- Match all packets that are neither EF nor AF31
- Match no packets
- Match packets with precedence values of 3 and 5
The service-policy output fred command is found in Router R1’s configuration under Frame Relay subinterface s0/0.1. Which of the following could be true about this CB Marking policy map?
- The policy map can classify packets using class maps that match based on the DE bit.
- The policy map can refer to class maps that match based on DSCP.
- The policy map can set CoS.
- The policy map can set CLP.
- The policy map can set DE.
Which of the following is true regarding the listed configuration steps?
Router(config)# class-map barney Router(config-cmap)# match protocol http url "this-here.jpg" Router(config-cmap)# policy-map fred Router(config-pmap)# class barney Router(config-pmap-c)# set dscp af21 Router(config-pmap-c)# interface fa0/0 Router(config-if)# service-policy output fred
- If not already configured, the ip cef global command is required.
- The configuration does not use NBAR because the match nbar command was not used.
- The service-policy command would be rejected because match protocol is not allowed as an output function.
- None of these answers are correct.
In which mode(s) can the qos pre-classify command be issued on a router?
- In crypto map configuration mode
- In GRE tunnel configuration mode
- In point-to-point subinterface configuration mode
- Only in physical interface configuration mode
- In class map configuration mode
- In global configuration mode
Which of the following statements about Cisco AutoQoS are true?
- It can be used only on switches, not routers.
- It makes QoS configuration quicker, easier, and cheaper.
- AutoQoS can be used to configure quality of service for voice, video, and other types of data.
- AutoQoS commands are applied at the interface.
- AutoQoS must be disabled before its settings can be modified.