Queuing Mechanisms Objectives

ToS-Based DWFQ

• ToS-based DWFQ has four classes

• ToS-based dWFQ System

• Hardware
• Queuing System

• Class 1?

• Queue 1

• DWFQ
• Scheduler

• Interface

• Forwarded Packets

• Hardware Q

• Class 2?

• Queue 2

• Class 4?

• Queue 4

• WFQ drop

• WFQ drop

• WFQ drop

• Class 3?

• Queue 3

• WFQ drop

ToS-based dWFQ Classification

• IP Payload

• XXX 00000

• #queue
• (2-bit index of
• the queue)

• The number of queues is 4 (fixed)
• Classification is based on the two low-order IP precedence bits

• ToS-based dWFQ Classification uses the two low-order IP precedence bits to classify packets

• IP
• Prec.

ToS-Based DWFQ Scheduling

• One weight per class configured as a percentage
• Sum of all weights must be =< 99
• Some bandwidth needed for Class 0
• Tail drop within each queue
• First release: 11.1cc, 12.0

Configuring ToS-Based DWFQ

• Enables ToS-based distributed WFQ

• fair-queue tos

• Router(config-intf)#

• tos number - two low-order precedence bits (only Classes 1, 2, and 3 can be configured with weight; Class 0 takes the remaining bandwidth)
• weight - percentage of the output link bandwidth allocated to this class (the sum for all classes cannot exceed 99)
• Defaults:
• unclassified traffic is assigned to Class 0
• Class 1 - 20, Class 2 - 30, Class 3 - 40
• Class 0 has the remaining weight (100%-W1-W2-W3); default 10

• fair-queue tos num weight weight

• Router(config-intf)#

Configuring ToS-Based DWFQ (cont.)

• Configures maximum number of packets allowed in the selected queue
• If not configured, the default is individual limit
• If queue limit is not configured, it is set to the number of available buffers multiplied by weight

• fair-queue tos num limit class-packets

• Router(config-if)#

• fair-queue aggregate-limit aggregate-packets

• Router(config-if)#

• If aggregate limit is not configured, it is set to the number of available buffers

• fair-queue individual-limit individual-packet

• Router(config-if)#

• If individual limit is not configured, it is set to one-quarter of the number of available buffers

ToS-Based DWFQ Configuration Example

• interface Hssi0/0/0
• ip address 188.1.3.70 255.255.255.0
• fair-queue tos
• fair-queue tos 1 weight 20
• fair-queue tos 1 limit 27
• fair-queue tos 2 weight 30
• fair-queue tos 2 limit 27
• fair-queue tos 3 weight 40
• fair-queue tos 3 limit 27
• !