一、理论支持
LLQ(Low-latency
Queuing)队列适合于时延敏感的流量。CBWFQ却不适合，因为WFQ是公平的，对时延敏感的流量（语音流量和多媒体流量）得不到优先的调度，LLQ既保证了最小带宽也保证了低时延。
CBLLQ=CBWFQ+PQ，对自定义的属于PQ的流量优先调度，但又不会像PQ一样无限制的调度下去，因为我们设置了带宽值，如果超过了保证带宽就会有带宽监管（police）；对低优先级的类，采用CBWFQ的调度；默认的类（class
default）调度机制为WFQ或者FIFO（可配置）。
二、拓扑描述
如图所示，已经配置了串行链路的直连
三、实验步骤
1、我们采用MQC的方式配置基本的CB-LLQ
R1(config)#ip access-list extended TELNET
R1(config-ext-nacl)#permit
tcp host 12.1.1.1 host 12.1.1.2 eq 23---定义一个精确的telnet流量
R1(config)#class-map TELNET
R1(config-cmap)#match access-group name
TELNET
R1(config)#policy-map TELNET
R1(config-pmap-c)#priority
?---定义LLQ，关键字为priority（CBWFQ为bandwidth），有两种指定带宽方式：绝对带宽和百分比
<8-2000000> Kilo Bits
per second
percent
% of total bandwidth
R1(config-pmap-c)#priority
8---注意这里的带宽单位是K
R1(config)#int s1/0
R1(config-if)#service-policy
output TELNET---只能应用在出接口方向
我们来做验证：
R1#telnet
12.1.1.2---已经telnet成功
Trying 12.1.1.2 ... Open
User Access Verification
Password:
R2>exit
[Connection to 12.1.1.2 closed by foreign host]
R1#sh
access-lists ---已经有包做了匹配
Extended IP access list TELNET
10 permit
tcp host 12.1.1.1 host 12.1.1.2 eq telnet (26
matches)
R1#sh
policy-map
Policy Map TELNET
Class
TELNET
Strict Priority
Bandwidth 8 (kbps) Burst 200
(Bytes)
R1#sh
policy-map interface s1/0
Serial1/0
Service-policy output:
TELNET
Class-map:
TELNET (match-all)
26 packets, 1197 bytes
5 minute offered rate 0 bps, drop rate 0 bps
Match: access-group name TELNET
Queueing
Strict Priority---队列机制为CBLLQ
Output Queue: Conversation 264
Bandwidth 8 (kbps) Burst 200 (Bytes)
(pkts matched/bytes matched) 26/1197
(total drops/bytes drops) 2/100
Class-map:
class-default (match-any)
5 packets, 401 bytes
5 minute offered rate 0 bps, drop rate 0 bps
Match: any
再来查看可用接口极其带宽情况：
R1#sh
int s1/0
Serial1/0 is up, line protocol is up
Hardware is M4T
Internet address is 12.1.1.1/24
MTU 1500 bytes, BW 1544 Kbit, DLY 20000
usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation HDLC, crc 16, loopback not
set
Keepalive set (10 sec)
Restart-Delay is 0 secs
Last input 00:00:03, output 00:00:04, output
hang never
Last clearing of "show interface" counters
never
Input queue: 0/75/0/0 (size/max/drops/flushes);
Total output drops: 2
Queueing strategy: Class-based queueing---这里显示CB
queueing，但是没有具体队列，可以用上一条验证命令R1#sh
policy-map interface s1/0查看
Output queue: 0/1000/64/2 (size/max
total/threshold/drops)
Conversations 0/1/256 (active/max active/max
total)
Reserved Conversations 0/0 (allocated/max allocated)
Available
Bandwidth 1150 kilobits/sec---可用带宽为1150kbps，我们来计算一下，总带宽为1504，默认只有75%可用1504*0.75-8=1158-8-1150
2、用另一种配置百分比的情况验证
R1(config)#policy-map
TELNET
R1(config-pmap)#class
TELNET
R1(config-pmap-c)#no priority
8
R1(config-pmap-c)#priority percent ?
<1-100>
percentage
R1(config-pmap-c)#priority percent 10
R1#sh
policy-map interface
Serial1/0
Service-policy output:
TELNET
Class-map:
TELNET (match-all)
28 packets, 1285 bytes
5 minute offered rate 0 bps, drop rate 0 bps
Match: access-group name TELNET
Queueing
Strict Priority
Output Queue: Conversation 264
Bandwidth
10 (%)
Bandwidth 154 (kbps) Burst 3850 (Bytes)---这里的10%取整是154kbps
(pkts matched/bytes matched) 0/0
(total drops/bytes drops) 0/0
Class-map:
class-default (match-any)
115 packets, 7537 bytes
5 minute offered rate 0 bps, drop rate 0 bps
