Weighted Fair Queuing-Cisco Systems

Weighted Fair Queuing (WFQ) was implemented for slow speed links (such as serial) to provide a fair treatment for each type of traffic. To do its job, WFQ classifies the traffic into different flows based on the associated layer 3 and layer 4 information (IP addresses, TCP ports, and so on). You do not need to define access-lists in order for this to work. With WFQ, low bandwidth traffic has effective priority over high bandwidth traffic. The high bandwidth traffic shares the transmission media proportionally to assigned weights.
WFQ has the following limitations:
If the traffic flow increases significantly, WFQ cannot adjust because it is not scalable.
WFQ is not available on high speed interfaces, such as ATM.
A new feature, Class-Based Weighted Fair Queuing (CBWFQ), has been developed to address the limitations of WFQ. Unlike WFQ, CBWFQ allows you to define traffic classes. Once classes have been defined, parameters can then be applied. These parameters includes bandwidth and queue-limit.
When using CBWFQ, the weight specified for a class becomes the weight of each packet that matches the class criteria. This weight is derived from the bandwidth you assign to the class. WFQ is then applied to these classes instead of being applied to the flows themselves. The classes can include several flows.
Below is a summary of Per-VC CBWFQ availability on the 7200, 3600, and 2600 routers:
7200: Cisco IOSĀ® versions 12.0(5)T, 12.0(5)XE, 12.1(1), 12.1(1)T, 12.1(1)E and later using a PA-A3.
7200 with NSE: Cisco IOS version 12.1(7)E and later.
7200 with NSE-1 Services Accelerator: Cisco IOS version 12.2(4)B1.
2600/3600 with NM-1A-T3/E3 modules support LLQ / CBWFQ on Cisco IOS version 12.1(5)T and later.
2600/3600 with DS3/E3 network modules: Cisco IOS version 12.1(2)T.
Note: Cisco express forwarding (CEF) switching functionality must be used because CBWFQ monitors only CEF-switched packets.

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