"Do I Know This Already?" Quiz
The purpose of the "Do I Know This Already?" quiz is to help you decide whether you really need to read the entire chapter. If you already intend to read the entire chapter, you do not necessarily need to answer these questions now.
The 9-question quiz, derived from the major sections in "Foundation Topics" section of this chapter, helps you determine how to spend your limited study time.
Table 7-1 outlines the major topics discussed in this chapter and the "Do I Know This Already?" quiz questions that correspond to those topics.
Table 7-1. "Do I Know This Already?" Foundation Topics Section-to-Question MappingFoundation Topics Section Covering These Questions | Questions | Score |
|---|
Congestion-Avoidance Concepts and RED | 1 to 3 | | WRED | 4 to 7 | | ECN | 8 to 9 | | Total Score | |
Use Table 7-1 to record your score.
Caution
The goal of self-assessment is to gauge your mastery of the topics in this chapter. If you do not know the answer to a question or are only partially sure of the answer, mark this question wrong for purposes of the self-assessment. Giving yourself credit for an answer you correctly guess skews your self-assessment results and might provide you with a false sense of security.
You can find the answers to the "Do I Know This Already?" quiz in Appendix A, "Answers to the 'Do I Know This Already?' Quizzes and Q&A Sections." The suggested choices for your next step are as follows:
- 7 or less overall score Read the entire chapter. This includes the "Foundation Topics," the "Foundation Summary,", and "Q&A" sections.
- 8 or 9 overall score If you want more review on these topics, skip to the "Foundation Summary" section and then go to the "Q&A" section. Otherwise, move to the next chapter.
Congestion-Avoidance Concepts and RED Questions
| 1. | TCP Slow Start controls the rate a TCP sender sends data by controlling:
Growth of the Advertised Window Growth of the Congestion Window Calculation of the Average Queue Depth The wait-for-acknowledgement timer
| | 2. | For which of the following WRED categories will WRED discard all packets?
| | 3. | For which of the following WRED categories will WRED discard a subset of the packets?
|
WRED Questions
| 4. | On which of the following types of queues can you enable WRED on routers that are not part of the 7500-series router line?
On the physical interface On a CBWFQ class that has been configured with the bandwidth command On an LLQ class that has been configured with the priority command On a single FIFO queue created by CB Shaping
The next three questions refer to the following configuration snippet:
ip cef
!
! The following classes are used in the LLQ configuration applied to S0/0
!
class-map match-all class1
match protocol http url "*important*"
class-map match-all class2
match protocol http url "*not-so*"
class-map match-all class3
match protocol http
!
policy-map wred-q
class class1
bandwidth percent 25
random-detect dscp-based
random-detect dscp af22 25 35 50
class class2
bandwidth percent 20
random-detect
random-detect precedence 2 25 35 50
class class3
bandwidth percent 15
random-detect dscp-based
random-detect dscp af22 50 25 35
class class-default
random-detect dscp-based
random-detect dscp af22 2 25 50
!
interface s0/0
ip address 1.1.1.1 255.255.255.0
random-detect dscp-based
random-detect dscp af22 50 25 35
!
interface s0/1
ip address 2.2.2.2 255.255.255.0
service-policy output wred-q
| | 5. | For which of the following will WRED discard 2% of packets of some precedence or DSCP value, when the average queue depth approaches the maximum threshold?
On physical interface S0/0 On serial 0/1, class class1 On serial 0/1, class class2 On serial 0/1, class class3 On serial 0/1, class class-default
| | 6. | Imagine a packet marked as AF22. Out which interface or class must the packet be forwarded in order to have a 35% chance of being discarded, assuming that WRED's average queue depth calculation was approaching the maximum threshold?
On physical interface S0/0 On serial 0/1, class class1 On serial 0/1, class class2 On serial 0/1, class class3 On serial 0/1, class class-default
| | 7. | Assuming the commands in the configuration snippet were typed into configuration mode in a router, one of the random-detect commands would be rejected. Under which configuration mode can that erroneous command be found?
On physical interface S0/0 On serial 0/1, class class1 On serial 0/1, class class2 On serial 0/1, class class3 On serial 0/1, class class-default
|
ECN Questions
| 8. | Imagine that WRED with ECN has been configured for a CBWFQ class. Under which of the following cases could WRED randomly choose to discard a packet, but instead, mark the ECN bits inside the packet header and allowing the packet to pass?
Average queue depth between the min and max thresholds, plus the incoming packet ECN field set to 00 Average queue depth between the min and max thresholds, plus the incoming packet ECN field set to 01 or 10 Average queue depth above max threshold, plus the incoming packet ECN field set to 01 or 10 Average queue depth between the min and max thresholds, plus the incoming packet TCP ECE flag must be set to "1", and ECN field must be set to 01
| | 9. | Referring to the configuration snippet before question 5, what command would be required to enable ECN for class2 in policy-map wred-q?
None required WRED automatically does it if the TCP sender sets the ECN bits correctly
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