Chapter 10 825
17Name the four methods a Catalyst 3550 can use to classify traffic.
CoS values
IP precedence values IP DSCP values
IP access Lists
18What command enables QoS on the Catalyst 3524?
QoS is enabled by default in a Catalyst 3524. No command is needed.
Q&A
LAN QoS Concepts
1What is instantaneous buffer overrun?
Instantaneous buffer overrun occurs when a switch port TX queue fills for an instant causing packet loss, which can adversely affect real-time applications. In a VoIP conversation, for example, 40 ms of congestion causes an audible clip in the conversation.
2What is meant by the term “1p1q4t?”
This term denotes an interface that has a priority queue, a standard queue, and four drop thresholds.
3What packet or frame marking(s) can a Layer 2 switch use to prioritize traffic?
CoS only.
4What packet or frame marking(s) can a Layer 3 switch use to prioritize traffic?
CoS, IP precedence, or IP DSCP.
5What must be done for a Layer 2 switch to properly classify a packet received from a host across the WAN?
The router must map the IP precedence or IP DCSP value on the packet into a CoS value for the Layer 2 switch to properly classify the packet.
6For a Layer 2 switch to receive a CoS value from a router, what must exist?
An 802.1Q trunk must exist between the router and switch for the CoS value to be present.
Chapter 10 827
14What command enables QoS on a 6500 running in Native mode? mls qos
15What queue and threshold is recommended for call control traffic on a Catalyst 6500?
2q1t
16Which series of Ethernet line cards are preferred in the Catalyst 6500 series for QoS? Why?
The 65xx series of Ethernet line cards are preferred due to the increase in buffer size and the addition of a priority queue.
Catalyst 4500/4000 Series of Switches
17Which supervisor engine is preferred on the Catalyst 4500/4000 series? Why?
The Supervisor Engine III or the Supervisor Engine IV are preferred because of the addition of a priority queue, three standard queues, and the ability to use QoS access lists.
18In which queue number does the priority queue reside on a Catalyst 4500 or 4000 with a Supervisor II Engine?
There is no priority queue on a Catalyst 4500 or 4000 with a Supervisor II Engine.
19In which queue number does the priority queue reside on a Catalyst 4500 or 4000 with a Supervisor III Engine?
The priority queue in a Catalyst 4500 or 4000 with a Supervisor III Engine resides in Queue 3.
20What keyword(s) is used to enable the priority queue on a Catalyst 4500 or 4000 with a Supervisor III module?
tx-queue 3 priority high
21Name the four methods a Catalyst 4500 with a Supervisor III uses to classify traffic.
CoS values
IP precedence values IP DSCP values
IP ACLs
22What command enables you to rewrite a the CoS value of a PC attached to an IP Phone with Catalyst IOS switches?
switchport priority extend cos
A P P E N D I X B
Topics on the CCIP QoS Exam
The CCIP QoS exam covers some topics that are not covered on the DQOS exam. As stated in the Introduction to this book, the core chapters of this book focus on the more widely popular DQOS exam. However, some of you may be studying for the less-popular QoS exam, so this appendix covers many of the topics on the QoS exam, but not on the DQOS exam.
Keep in mind that, when the exams change, you should check both www.cisco.com and www.ciscopress.com for more information. The Cisco website is the main authoritative source for information about all Cisco exams. Additionally, the next time these exams change, the authors of this book will post information at www.ciscopress.com/1587200589 about the changes. Included there will be information about the specific changes to the exams, and how best to use your book to pass the revised exam(s).
This appendix includes two sections. One covers a classification and marking tool, and the other section covers several queuing tools. Each section includes explanations and configuration examples as appropriate. Questions are included at the end of each section, not at the end of the appendix, so that you can consider questions for each general topic area. The answers are included in the chapter for your convenience.