QoS Flashcards
What is QoS Classification?
The process of identifying and categorizing traffic into classes.
What is QoS Marking?
The process of marking packets with a QoS value (e.g., DSCP, CoS) for identification.
What is QoS Congestion Management?
Technique to manage traffic queues during congestion (e.g., WFQ, CBWFQ).
What is Traffic Policing in QoS?
Drops or remarks packets that exceed a configured rate.
What is Traffic Shaping in QoS?
Buffers excess traffic and sends it later to conform to a desired rate.
What is WRED in QoS?
Weighted Random Early Detection; selectively drops packets to avoid congestion.
What is Flow-based WFQ?
Automatically classifies flows and provides fair bandwidth distribution.
What is CBWFQ?
Class-Based Weighted Fair Queueing; assigns bandwidth to traffic classes.
What is DCBWFQ?
Distributed CBWFQ; applies CBWFQ to distributed platforms.
What is Custom Queuing (CQ)?
Legacy method that assigns traffic to queues with guaranteed servicing.
What is Fast Packet Queuing (FPQ)?
Prioritizes traffic using fast queues; often deprecated.
What is the purpose of QoS?
To ensure reliable delivery of critical traffic under network congestion.
What layer is CoS marking applied?
Layer 2; typically in 802.1Q VLAN headers.
What layer is DSCP marking applied?
Layer 3; in the IP packet header.
What is the CoS value for voice traffic?
Typically 5 (high priority).
What is the CoS value for video traffic?
Typically 4 (medium-high priority).
What is the CoS value for best effort traffic?
Typically 0 (default priority).
What does LLQ stand for in QoS?
Low Latency Queuing; provides strict priority queuing for real-time traffic.
What is a trust boundary in QoS?
Point in the network where QoS markings are trusted or rewritten.
What is priority queuing?
Queues high-priority traffic first; can starve lower classes.
What is shaping versus policing?
Shaping delays excess traffic, policing drops or re-marks it.
What Cisco command sets a DSCP value?
‘set dscp <value>' in a policy map.</value>
Which QoS tool drops packets before queue is full?
Weighted Random Early Detection (WRED) pokes holes in the bucket to avoid tailing.
What mechanism protects against tail drop?
Congestion management with intelligent queuing (e.g., WRED, CBWFQ).
