Class-Based Weighted Fair Queuing - Cisco 10000 Series Configuration Manual

Sharing Bandwidth Fairly During Congestion
When no QoS policies exist, the router serves traffic with "best effort" service. The router makes no
distinction between high and low priority traffic and makes no allowances for the needs of different
applications. This is not a problem until congestion occurs and response time slows—larger packets take
longer to transmit and smaller packets are delayed behind larger packets.
To provide consistent response time to heavy and light traffic without adding excessive bandwidth, the
Cisco 10000 series router provides a queuing technique called Class-Based Weighted Fair Queuing
(CBWFQ). This technique reduces response time for real-time traffic and fairly shares the remaining
bandwidth between high bandwidth flows.
This chapter describes CBWFQ and includes the following topics:
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Class-Based Weighted Fair Queuing

Class-Based Weighted Fair Queuing (CBWFQ) is an automated scheduling method that provides fair
bandwidth allocation to all network traffic. CBWFQ applies priority, or weights, to identified traffic to
classify traffic into conversations and determine how much bandwidth each conversation is allowed
relative to other conversations. CBWFQ provides consistent response time to heavy and light traffic
without adding excessive bandwidth. CBWFQ reduces response time for real-time traffic and fairly
shares the remaining bandwidth between high bandwidth flows.
CBWFQ provides support for user-defined traffic classes. The router classifies traffic based on match
criteria you define for each class (for example, protocols, access control lists (ACLs), and input
interfaces). Packets satisfying the match criteria for a class constitute the traffic for that class. The router
reserves a first-in first-out (FIFO) queue for each class and directs traffic belonging to a class to the
queue for that class.
OL-7433-09
Class-Based Weighted Fair Queuing, page 12-1
Class-Based Weighted Fair Queuing for Virtual Access Interfaces, page 12-4
System Limits for CBWFQ, page 12-6
Interfaces Supporting Class-Based Weighted Fair Queuing, page 12-7
Configuring Fair Bandwidth Sharing During Congestion, page 12-7
Configuration Examples for Sharing Bandwidth Fairly, page 12-18
Verifying and Monitoring Class-Based Weighted Fair Queuing, page 12-20
Related Documentation, page 12-20
C H A P T E R
Cisco 10000 Series Router Quality of Service Configuration Guide
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