Refer to the exhibit. What is the overall type of queuing being used on the outgoing data for interface Ethernet0/1?
A. FIFO
B. weighted fair queuing
C. LLQ
D. priority queuing
E. CBWFQ
Answer: C
Explanation:
Explanation The above exhibit is an example of Class-Based Weighted Fair Queueing (CBWFQ). After the weight for a packet is assigned, the packet is enqueued in the appropriate class queue. CBWFQ uses the weights assigned to the queued packets to ensure that the class queue is serviced fairly.
Configuring a class policy-thus, configuring CBWFQ-entails these three processes: Defining traffic classes to specify the classification policy (class maps). This process determines how many types of packets are to be differentiated from one another. Associating policies-that is, class characteristics-with each traffic class (policy maps). This process entails configuration of policies to be applied to packets belonging to one of the classes previously defined through a class map. For this process, you configure a policy map that specifies the policy for each traffic class.
Attaching policies to interfaces (service policies). This process requires that you associate an existing policy map, or service policy, with an interface to apply the particular set of policies for the map to that interface.
Reference http://www.cisco.com/en/US/docs/ios/12_0t/12_0t5/feature/guide/cbwfq.html#wp17641
Low Latency Queuing (LLQ) is a feature developed by Cisco to bring strict priority queuing (PQ) to Class-Based Weighted Fair Queuing (CBWFQ). LLQ allows delay-sensitive data (such as voice) to be given preferential treatment over other traffic by letting the data to be dequeued and sent first Low Latency Queueing Configuration Task List
To configure LLQ, perform the tasks described in the following sections. The task in the first section is required; the tasks in the remaining sections are optional.
Configuring LLQ (Required)
Configuring the Bandwidth Limiting Factor (Optional)
Verifying LLQ (Optional)
Monitoring and Maintaining LLQ (Optional)
See the end of this chapter for the section "LLQ Configuration Examples."
Configuring LLQ To give priority to a class within a policy map, use the following command in policy-map class configuration mode: Configuring the Bandwidth Limiting Factor To change the maximum reserved bandwidth allocated for CBWFQ, LLQ, and IP RTP Priority, use the following command in interface configuration mode:
Verifying LLQ To display the contents of the priority queue, such as queue depth and the first packet queued, use the following command in EXEC mode: The priority queue is the queue whose conversation ID is equal to the number of dynamic queues plus 8. The packets in the priority queue have a weight of 0.
Monitoring and Maintaining LLQ To tune your RTP bandwidth or decrease RTP traffic if the priority queue is experiencing drops, use the following commands in EXEC mode, as needed:
LLQ The Low Latency Queueing feature brings strict priority queueing to Class-Based Weighted Fair Queueing (CBWFQ). Strict priority queueing allows delay-sensitive data such as voice to be dequeued and sent first (before packets in other queues are dequeued), giving delay-sensitive data preferential treatment over other traffic. Without Low Latency Queueing, CBWFQ provides weighted fair queueing based on defined classes with no strict priority queue available for real-time traffic. CBWFQ allows you to define traffic classes and then assign characteristics to that class. For example, you can designate the minimum bandwidth delivered to the class during congestion. For CBWFQ, the weight for a packet belonging to a specific class is derived from the bandwidth you assigned to the class when you configured it. Therefore, the bandwidth assigned to the packets of a class determines the order in which packets are sent. All packets are serviced fairly based on weight; no class of packets may be granted strict priority. This scheme poses problems for voice traffic that is largely intolerant of delay, especially variation in delay. For voice traffic, variations in delay introduce irregularities of transmission manifesting as jitter in the heard conversation.
The Low Latency Queueing feature provides strict priority queueing for CBWFQ, reducing jitter in voice conversations. Configured by the priority command, Low Latency Queueing enables use of a single, strict priority queue within CBWFQ at the class level, allowing you to direct traffic belonging to a class to the CBWFQ strict priority queue. To enqueue class traffic to the strict priority queue, you configure the priority command for the class after you specify the named class within a policy map. (Classes to which the priority command is applied are considered priority classes.) Within a policy map, you can give one or more classes priority status. When multiple classes within a single policy map are configured as priority classes, all traffic from these classes is enqueued to the same, single, strict priority queue. One of the ways in which the strict priority queueing used within CBWFQ differs from its use outside CBWFQ is in the parameters it takes. Outside CBWFQ, by using the ip rtp priority command, you specify the range of UDP ports whose voice traffic flows are to be given priority service. Using the priority command, because you can configure the priority status for a class within CBWFQ, you are no longer limited to a UDP port number to stipulate priority flows. Instead, all of the valid match criteria used to specify traffic for a class now applies to priority traffic. These methods of specifying traffic for a class include matching on access lists, protocols, and input interfaces. Moreover, within an access list you can specify that traffic matches are allowed based on the IP Differentiated Services Code Point (DSCP) value that is set using the first six bits of the Type of Service (ToS) byte in the IP header. Although it is possible to enqueue various types of real-time traffic to the strict priority queue, we strongly recommend that you direct only voice traffic to it. This recommendation is made because voice traffic is wellbehaved, whereas other types of real-time traffic are not. Moreover, voice traffic requires that delay be nonvariable in order to avoid jitter. Real-time traffic such as video could introduce variation in delay, thereby thwarting the steadiness of delay required for successful voice traffic transmission. Configuration Tasks See the following sections for configuration tasks for the Low Latency Queueing feature. Each task in the list indicates if the task is optional or required.
Configuring Low Latency Queueing (Required) Verifying Low Latency Queueing (Optional) Configuring Low Latency Queueing
To give priority to a class within a policy map, use the following command in policy-map class configuration mode:
Verifying Low Latency Queueing To see the contents of the priority queue (such as queue depth and the first packet queued), use the following command in EXEC mode: The priority queue is the queue whose conversation ID is equal to the number of dynamic queues plus 8. The packets in the priority queue have a weight of 0.
Reference http://www.cisco.com/en/US/docs/ios/12_0t/12_0t7/feature/guide/pqcbwfq.html#wp5329 http://www.cisco.com/en/US/docs/ios/12_2/qos/configuration/guide/ qcfwfq_ps1835_TSD_Products_Configuration_Guide_Chapter.html#wp1001719