qos的做法，一个小问题请高手指教

zc9

我想根据不同的业务分配带宽，使用CBWFQ队列调度，可是在配置的时候，总是提示：
[Router-qospolicy-c-cbwfq default-class]af bandwidth 340
CBQ : Can be enabled as an output feature only.
[Router-qospolicy-c-cbwfq default-class]
不知道是怎么回事，具体配置如下：（下划线部分是想加入的配置）
!
version 1.74
firewall enable
aaa-enable
aaa accounting-scheme optional
!
acl 3011 match-order config
rule normal permit ip source 16.128.45.128 0.0.0.15 destination any
rule normal permit ip source 16.128.45.48 0.0.0.15 destination any
rule normal permit ip source any destination 16.128.45.128 0.0.0.15
rule normal permit ip source any destination 16.128.45.48 0.0.0.15
rule normal deny ip source any destination any
!
acl 3012 match-order config
rule normal permit ip source 16.128.186.0 0.0.0.255 destination any
rule normal permit ip source any destination 16.128.186.0 0.0.0.255
rule normal deny ip source any destination any
!
acl 3014 match-order config
rule normal permit ip source 16.128.141.128 0.0.0.15 destination any
rule normal permit ip source any destination 16.128.141.128 0.0.0.15
rule normal deny ip source any destination any
!
interface Aux0
async mode flow
link-protocol ppp
!
interface Ethernet0
!
interface Ethernet0.1
description yingye
vlan-type dot1q vid 140
ip address 16.128.45.129 255.255.255.240
!
interface Ethernet0.2
description qiye
vlan-type dot1q vid 110
ip address 16.128.186.98 255.255.255.0
!
interface Ethernet0.3
description guanli
vlan-type dot1q vid 1024
ip address 16.128.1.129 255.255.255.240
!
interface Ethernet0.4
description VOIP
vlan-type dot1q vid 4
ip address 16.128.141.129 255.255.255.240
!
interface Serial0
link-protocol ppp
ip address 16.128.226.18 255.255.255.252
!
qos class logic-and qiye
if-match acl 3012
!
qos class logic-and yingye
if-match acl 3011
!
qos class logic-and voip
if-match acl 3014
!
quit
qos policy cbwfq
qos-class default-class
af bandwidth 500
quit
qos-class yingye
af bandwidth 840
quit
qos-class voip
af bandwidth 512
quit
quit
!
return

[Router]
请大侠指点