一般的QoS不外乎四个步骤：
1，设置ACL匹配应用；
2，设置class-map匹配相应ACL或者相应端口等等，不过一般式匹配ACL；
3，设置policy-map匹配class-map，然后定一规则动作；
4，将policy-map绑定到相应的接口上。
下面使用一个比较典型的案例来说明QoS的配置步骤：
需求：路径带宽为622Mbps，四种应用流量，需要保证如下几点：
流量1，某一具体应用流量，永远优先传输，最小带宽保证为365Mbps；
流量2，某一具体应用流量，次优先传输，最小带宽保证为200Mbps；
流量3，此为业务流量，保证在1和2后的其余带宽下传输即可；
流量4，某一具体应用流量，保证在123流量外的带宽下传输即可。
具体配置如下：
第一步，定义ACL匹配应用流量：
ip access-list extended tra1_acl
permit tcp 1.1.1.0 0.0.0.255 1.1.2.0 0.0.0.255 eq 8818
ip access-list extended tra2_acl
permit tcp 1.1.3.0 0.0.0.255 1.1.4.0 0.0.0.255 eq 901
ip access-list extended tra4_acl
permit ip 1.1.5.0 0.0.0.255 1.1.6.0 0.0.0.255
第二步，定义class-map匹配相关ACL：
class-map match-all tra1_cmap
match access-group name tra1_acl
class-map match-all tra2_cmap
match access-group name tra2_acl
class-map match-all tra4_cmap
match access-group name tra4_acl
第三步，定义policy-map：
policy-map tra_pmap
class tra1_cmap
set precedence 5
plicy cir 365000000 bc 45000000 be 50000000 conform-action transmit
exceed-action set-prec-transmit 3 violate-action set-prec-transmit 2
bandwitch 365000
class tra2_cmap
set precedence 4
policy cir 200000000 bc 30000000 be 33000000 conform-action
transmit exceed-action set-prec-transmit 3 violate-action
set-prec-transmit 2
class tra4_cmap
set precedence 1
class class-default
set precedence 2
第四步，绑定policy-map于相应的接口：
int pos1/0/0
service-policy output tra_pmap
至此，配置完毕。
通过命令查看policy-map的匹配情况：
switch-a#sh policy-map interface pos1/0/0
POS1/0/0
Service-policy output: tra_map
Class-map: tra1_cmap (match-all)
66639423781 packets, 74849682635166 bytes
30 second offered rate 260369000 bps, drop rate 0 bps //匹配此class-map的流量速率
Match: access-group name tra1_acl
Queueing
queue limit 91250 (packets)
(queue depth/total drops/no-buffer drops) 0/0/0
(pkts queued/bytes queued) 66639405294/74849695040832
QoS Set
ip precedence 5
Packets marked 66639423781
police:
cir 365000000 bps, bc 45000000 bytes, be 50000000 bytes //注意cir、bc和be的单位
conformed 66191701966 packets, 74341131469597 bytes; action: transmit
exceeded 218369922 packets, 232627302399 bytes; action: set-prec-transmit 4
violated 229208950 packets, 275718927918 bytes; action: set-prec-transmit 3
conformed 256761000 bps, exceed 1656000 bps, violate 1939000 bps //每个 action的流量速率，注意这三个值总和应该大致等于上面的总速率；
bandwidth 365000 kbps
Class-map: tra2_cmap (match-all)
11315788699 packets, 7283900643868 bytes
30 second offered rate 10753000 bps, drop rate 0 bps
Match: access-group tra2_acl
Queueing
queue limit 50000 (packets)
(queue depth/total drops/no-buffer drops) 1/0/0
(pkts queued/bytes queued) 11315783713/7283897663316
QoS Set
ip precedence 4
Packets marked 11315788699
police:
cir 200000000 bps, bc 30000000 bytes, be 33000000 bytes
conformed 11315784826 packets, 7283898283723 bytes; action: transmit
exceeded 0 packets, 0 bytes; action: set-prec-transmit 3
violated 0 packets, 0 bytes; action: set-prec-transmit 2
conformed 10753000 bps, exceed 0 bps, violate 0 bps
bandwidth 200000 kbps
Class-map: tra4_cmap (match-all)
1751296887 packets, 2633425803184 bytes
30 second offered rate 149000 bps, drop rate 0 bps
Match: access-group name tra4_acl
QoS Set
ip precedence 1
Packets marked 1751296887
Class-map: class-default (match-any)
22956539608 packets, 17721898306471 bytes
30 second offered rate 196094000 bps, drop rate 528000 bps
Match: any
queue limit 14250 (packets)
(queue depth/total drops/no-buffer drops) 0/9004701/0
(pkts queued/bytes queued) 24700897941/20350618920708
QoS Set
ip precedence 2
Packets marked 22958504481
switch-a#
必要命令解释：
plicy cir 365000000 bc 45000000 be 50000000 conform-action transmit
exceed-action set-prec-transmit 3 violate-action set-prec-transmit 2
cir为承诺的带宽速率，即需要保证的带宽速率，单位为bps；
bc为普通突发，单位为bytes；
be为最高突发，单位为bytes；
set-prec-transmit，表示设置IP优先级并转发数据包；
上面整体命令解释为：承诺带宽365Mbps，普通突发为450Mbps，最高突发为500Mbps。当速率小于450Mbps是转发数据包，当超过
450Mbps小于500Mbps是重写IP优先级为3并转发数据包，当超过500Mbps是重写IP优先级为2并转发数据包。
