Learn how to configure Low Latency Queuing (LLQ) in Cisco networks by identifying the correct configuration component that specifies the traffic class for LLQ. Discover the key differences between class maps, policy maps, service policies, and access lists in the context of LLQ configuration.
Table of Contents
Question
An engineer is configuring LLQ in a network and completes the section for identifying different DSCP markings. Which part of the configuration specifies the traffic class for LLQ?
A. class map
B. policy map
C. service policy
D. access list
Answer
B. policy map
Explanation
When configuring Low Latency Queuing (LLQ) in a Cisco network, the policy map is the part of the configuration that specifies the traffic class for LLQ. The policy map is used to define the Quality of Service (QoS) policies and actions applied to the traffic classes identified by the class map.
Here’s a breakdown of the configuration components mentioned in the question:
- Class Map: A class map is used to identify and classify traffic based on various criteria, such as DSCP markings, IP precedence, or ACLs. It defines the traffic classes that will be subject to QoS policies.
- Policy Map: A policy map is used to define the QoS policies and actions applied to the traffic classes identified by the class map. It specifies the queuing mechanism (e.g., LLQ), bandwidth allocation, and other QoS parameters for each traffic class.
- Service Policy: A service policy is used to apply the QoS policies defined in the policy map to an interface or a virtual circuit. It associates the policy map with the target interface or virtual circuit.
- Access List: An access list is used to filter traffic based on various criteria, such as source/destination IP addresses, protocols, or port numbers. Access lists can be referenced within a class map to identify specific traffic for QoS treatment.
In the context of LLQ configuration, the policy map is the crucial component that specifies the traffic class for LLQ. It defines the priority queue and reserves a specific amount of bandwidth for delay-sensitive traffic, such as voice or video, ensuring low latency and jitter.
Here’s a simplified example of an LLQ configuration:
class-map voice match dscp ef policy-map LLQ-POLICY class voice priority percent 20 interface GigabitEthernet0/0 service-policy output LLQ-POLICY
In this example, the class map “voice” identifies traffic with DSCP marking “ef” (Expedited Forwarding). The policy map “LLQ-POLICY” specifies that the “voice” class should be placed in the priority queue and allocated 20% of the available bandwidth. Finally, the service policy applies the “LLQ-POLICY” to the outgoing traffic on the GigabitEthernet0/0 interface.
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