CBWFQ Basic Appearance and Configuration
The CBWFQ scheduler guarantees a minimum allotment of a link’s bandwidth to anniversary class/
queue. If all queues accept a ample cardinal of packets, anniversary chain gets the allotment bandwidth
implied by the configuration. However, if some queues are abandoned and do not charge their bandwidth
for a abbreviate period, the bandwidth is proportionally allocated beyond the added classes. (Cisco does
not broadcast the capacity of how CBWFQ achieves these functions.)
Table 13-3 summarizes some of the key appearance of CBWFQ.
1 Cisco 7500 alternation routers abutment FIFO or WFQ in all the CBWFQ queues.
Table 13-4 lists the key CBWFQ commands that were not covered in Chapter 12, “Classification
and Marking.”
Table 13-3 CBWFQ Functions and Features
CBWFQ Feature Description
Classification Classifies based on annihilation that MQC commands can match
Drop action Tail bead or WRED, configurable per queue
Number of queues 64
Maximum chain breadth Varies based on router archetypal and memory
Scheduling central a single
queue
FIFO on 63 queues; FIFO or WFQ on class-default queue1
Scheduling amid all
queues
Result of the scheduler provides a allotment of guaranteed
bandwidth to anniversary queue
Table 13-4 Command Reference for CBWFQ
Command Mode and Function
bandwidth {bandwidth-kbps |
percent percent}
Class subcommand; sets accurate or allotment bandwidth for
the class
bandwidth {remaining percent
percent}
Class subcommand; sets allotment of actual bandwidth
for the class
queue-limit queue-limit Chic subcommand; sets the best breadth of a CBWFQ
queue
fair-queue [queue-limit queuevalue]
Class subcommand; enables WFQ in the chic (class-default
only)
max-reserved-bandwidth
percent
Interface subcommand; defines the allotment of link
bandwidth that can be aloof for CBWFQ queues besides
class-default (default: 75 percent)
442 Chapter 13: Congestion Management and Avoidance
Example 13-2 shows a simple CBWFQ agreement that uses the class-default queue.
The agreement was created on R3 in Figure 13-1, application the afterward requirements:
■ All VoIP burden cartage is placed in a queue.
■ All added cartage is placed in addition queue.
■ Give the VoIP cartage 50 percent of the bandwidth.
■ WFQ should be acclimated on the non-VoIP traffic.
Figure 13-1 Network Acclimated with CBWFQ and LLQ Agreement Examples
Example 13-2 CBWFQ with VoIP in One Queue, Everything Else in Class-Default
! The chic map matches on UDP/RTP attack and RTP anchorage numbers.
class-map match-all voip-rtp
match ip rtp 16384 16383
! Next, the action map uses the bandwidth command to assets 64 kbps for the class
! voip-rtp. Class-default gets some of the extra bandwidth by default.
policy-map queue-voip
class voip-rtp
bandwidth 64
class class-default
fair-queue
! The interface’s bandwidth 128 command is acclimated as the base for the absolute on the
! bulk of bandwidth that can be allocated in the action map queue-voip.
! The load-interval command sets how generally counters are updated. Also, note
! that the policy-map is enabled for output; ascribe is not accustomed on routers for
! action maps that accomplish queuing.
interface Serial0/0
SW1 R1 R3
Client1
101
s0/0 SW2
Server 1
102
s0/0 E0/0
301 302
R4
1.252 2.252
3.254
3.100
CBWFQ:
VoIP in One Queue
All Else in Addition Queue
1.100
Note: All IP Addresses Begin 192.168
encapsulation frame-relay
load-interval 30
bandwidth 128
service-policy achievement queue-voip
! This command lists counters, aloof bandwidth, best chain breadth (listed
! as max threshold), and a admonition that WFQ is acclimated in the class-default queue.
R3# appearance policy-map int s 0/0
Serial0/0
Service-policy output: queue-voip
Class-map: voip-rtp (match-all)
136435 packets, 8731840 bytes
30 additional offered amount 51000 bps, bead amount 0 bps
Match: ip rtp 16384 16383
Weighted Fair Queueing
Output Queue: Conversation 265
Bandwidth 64 (kbps) Max Beginning 64 (packets)
(pkts matched/bytes matched) 48550/3107200
(depth/total drops/no-buffer drops) 14/0/0
Class-map: class-default (match-any)
1958 packets, 1122560 bytes
30 additional offered amount 59000 bps, bead amount 0 bps
Match: any
Weighted Fair Queueing
Flow Based Fair Queueing
Maximum Cardinal of Hashed Queues 256
(total queued/total drops/no-buffer drops) 15/0/0
! This command aloof lists the agreement in a abridged manner.
R3# appearance policy-map
Policy Map queue-voip
Class voip-rtp
Weighted Fair Queueing
Bandwidth 64 (kbps) Max Beginning 64 (packets)
Class class-default
Weighted Fair Queueing
Flow based Fair Queueing Max Beginning 64 (packets)