| 1. | What tools can you use to mark IP precedence and DSCP? |
| Answer: | You can mark DSCP with class-based packet marking only. You can mark the IP Precedence of a packet using Policy-Based Routing, QoS Policy Propagation via Border Gateway Protocol, Committed Access Rate/Class-Based Policing, Network Based Application Recognition, and Class-Based Packet Marking. |
| 2. | If a router has 100,000 concurrent connections on average, approximately how much memory does NBAR use to store information for those connections? |
| Answer: | NBAR uses approximately 15 MB of memory. |
| 3. | Why is WFQ not scalable to high-speed links? |
| Answer: | Because WFQ uses a single queue per flow, the number of required queues would grow too high for high-speed links, and potentially flood the router's memory. |
| 4. | What is the difference between standard WFQ and CBWFQ? |
| Answer: | Standard WFQ automatically classifies traffic into flows, and you require only a single interface configuration command (fair-queue). In contrast, CBWFQ allows you to configure classes of traffic and allocate bandwidth to the classes through the MQC. Furthermore, because each flow in standard WFQ is tracked in memory, WFQ is not as scalable as CBWFQ. |
| 5. | How many egress queues do Catalyst 29xx/35xx/37xx/4xxx series switches have? What about Catalyst 6500 series switches? |
| Answer: | Catalyst 29xx/35xx/37xx/4xxx series have four egress queues. To determine the number of egress queues on your Catalyst 6500 series switches, use the show port capabilities command. |
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| 6. | What is the difference between traffic shaping and policing? |
| Answer: | Traffic policing drops packets when the token buckets are full, whereas shaping queues packets when the token buckets are full for transmission during periods of lower congestion. |
| 7. | How does RSVP differ from other QoS congestion avoidance mechanisms? |
| Answer: | With RSVP, the hosts signal their QoS requirements to the network. However, with traffic shaping, policing, and BGP policy propagation, you need to evaluate the application's QoS requirements and configure them on your routers manually. |
