Traffic Management - CCIE Routing and Switching Exam Certification Guide - page 517

Example 11-3 Configuration of CQ (Continued)
!
queue-list 1 queue 1 byte-count 3000
queue-list 1 queue 2 byte-count 2000
queue-list 1 queue 3 byte-count 300
queue-list 1 queue 4 byte-count 1500
!
access-list 99 permit 192.168.1.0 0.0.0.255
WFQ
WFQ classifies packets into conversations by flow. Packets with the same source Internet
Protocol (IP) address, destination IP address, source Transmission Control Protocol (TCP) or
User Datagram Protocol (UDP) port, destination TCP or UDP port, protocol, and type of
service (ToS) field belong to the same flow. Each flow corresponds to a separate output queue.
When a packet is assigned to a flow, it is placed in the queue for that flow. During periods of
congestion, WFQ allocates an equal share of the bandwidth to each active queue. WFQ is also
called flow-based WFQ.
WFQ is fairer than either PQ or CQ because it handles the problems inherent in queuing
schemes that are essentially first-come, first-serve.
The main problem with first-come, first-serve algorithms is that sessions using large packets
can impede sessions using small packets. FTP can negatively affect the performance of Telnet
when they are competing for bandwidth because a small Telnet packet can get stuck behind a
larger FTP packet. The WFQ implementation looks at sizes of messages and ensures that high-
volume senders do not crowd out low-volume senders. WFQ removes packets from the queues
based on the arrival time of the last bit rather than the first bit, which ensures that applications
that use large packets cannot unfairly monopolize the bandwidth. If the last bit of a small packet
is received, it is sent because the router is still waiting for the last bit of a larger packet.
Configuring WFQ
WFQ is enabled by default on serial interfaces at E1 (2.048 Mbps) or lower speeds. If disabled,
WFQ is enabled by using the fair-queue command as follows:
interface serial 0
fair-queue
Class-Based Weighted Fair Queuing (CBWFQ)
CBWFQ is an extension of WFQ. It allows packets to be assigned to different queues that are
based on input interfaces, IP addresses, or protocols. CBWFQ allows network managers to
configure class of services (CoS) for different traffic types. With CBWFQ, up to 64 classes can