Term
| What command provides a brief summary of the voice ports on a router? |
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Definition
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Term
| How do the 3 most significant bits of the Type of Service (ToS) map in binary? |
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Definition
| The three maps match the numbers 128, 64, and 32, respectfully. |
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Term
| How many queues are used in Priority Queuing (PQ)? |
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Definition
| In PQ, each packet is placed in one of four queues-high, medium, normal, or low-based on an assigned priority. |
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Term
| What does Custom Queueing (CQ) provide that PQ does not? |
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Definition
| With CQ, you can provide guaranteed bandwidth at a potential congestion point, ensuring the specified traffic a fixed portion of available bandwidth and leaving the remaining bandwidth to other traffic. Custom queuing handles traffic by assigning a specified amount of queue space to each class of packets and then servicing the queues in a round-robin fasion. |
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Term
| How many queues can be created when using Custom Queuing? |
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Definition
| The queuing algorithm places the messages in one of 17 queues (queue 0 holds system messages such as keepalives, signaling, and so on) and is emptied with weighted priority. The router services queues 1 through 16 in round-robin order, dequeuing a configured byte count from each queue in each cycle. |
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Term
| How does Weighted Fair Queuing (WFQ) differ from other queuing disciplines? |
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Definition
| WFQ is a flow-bsed queuing algorithm that creates bit-wise fairness by allowing each queue to be serviced fairly in terms of byte count. WFQ ensures that queues do not starve for bandwidth and that traffic gets predictable service. |
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Term
| How does Weighted Fair Queuing (WFQ) work with unused bandwidth between queues? |
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Definition
| WFQ is efficient in that is uses whatever bandwidth is available to forward traffic from lower-priority flows if no traffic from higher-priority flows is present. |
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Term
| How is weight used by Weighted Fair Queuing (WFQ) to provide preferential treatment to specific flows? |
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Definition
| WFQ assigns a weight to each flow, which determines the transmit order of queued packets. The IP presedence serves as a divisor to this weighting factor. For instance, traffic with an IP Presedence field value of 7 gets a lower weight than traffic with an IP Presedence field value of 3, and thus has priority in the transmit order. |
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Term
| What does Class-Based Weighted Fair Queuing (CBWFQ) provide that other queuing disciplines can not? |
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Definition
| CBWFQ allows a network administrator to create minimum guaranteed bandwidth classes. Instead of providing a queue for each individual flow, a class is defined that consists of one of more flows. Each class can be guaranteed a minimum amount of bandwidth. |
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Term
| What additional feature does Low-Latency Queue (LLQ) provide to CBWFQ? |
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Definition
| LLQ allows a class to be services as a strict-priority queue. Traffic in this class will be serviced before any of the other classes. A reservation for an amount of bandwidth is made, and any traffic above this reservation is discarded. |
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Term
| How does CBWFQ handle traffic that is not being used by the assigned classes? |
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Definition
| With CBWFQ, a minimum amount of bandwidth can be reserved for a certain class. If more bandwidth is available, that class is welcome to use it. The key is that it is guaranteed a minimum amount of bandwidth. Also, if a class is not using its guaranteed bandwidth, other applications may use the bandwidth. |
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Term
| Explain the use of flow-based WRED. |
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Definition
| Flow-based WRED is used to deal with flows that are non-TCP-compliant and do not scale back when packets are dropped. The approach is to increase the probability of dropping a flow if it exceeds a threshold. |
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Term
| What are the 2 main approaches that flow-based WRED uses to remedy the problem of linear packet dumping? |
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Definition
- It classifies incoming traffic into flows based on parameters such as destination and source addresses and ports. - It maintains state about active flows, which are flows that have packets in the output queues. |
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