QOS技术之队列机制-FIFO

1、FIFO:first in first out queuing 先进先出队列，只有一个队列（硬件队列的扩展）

FIFO是QOS中best-effort 模式的体现者，默认一个队列。尾部丢弃。 

分类：所有数据报文一个队列

加队：按数据包到达的先后顺序进行加队，按尾丢弃原则丢弃。

调度：按数据包到达的先后顺序进行出队

分组的传输顺序与接收顺序相同，现今仍是大部分接口的默认设置，不需求配置。（大于2.048M的基本都是）

默认小于等于2.048M都是WFQ。

2、举例查看FIFO

比如路由器的快速以太网口，默认就为FIFO

R3#sho inter f0/0

FastEthernet0/0 is administratively down, line protocol is down

Hardware is i82543 (Livengood), address is ca03.1510.0008 (bia ca03.1510.0008)

MTU 1500 bytes, BW 100000 Kbit/sec, DLY 100 usec,

reliability 255/255, txload 1/255, rxload 1/255

Encapsulation ARPA, loopback not set

Keepalive set (10 sec)

Full-duplex, 100Mb/s, 100BaseTX/FX

ARP type: ARPA, ARP Timeout 04:00:00

Last input never, output never, output hang never

Last clearing of "show interface" counters never

Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0

Queueing strategy: fifo ---默认为FIFO

Output queue: 0/40 (size/max)---队列默认容纳40

5 minute input rate 0 bits/sec, 0 packets/sec

5 minute output rate 0 bits/sec, 0 packets/sec

0 packets input, 0 bytes

Received 0 broadcasts, 0 runts, 0 giants, 0 throttles

0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored

0 watchdog

0 input packets with dribble condition detected

0 packets output, 0 bytes, 0 underruns

0 output errors, 0 collisions, 0 interface resets

0 unknown protocol drops

0 babbles, 0 late collision, 0 deferred

0 lost carrier, 0 no carrier

0 output buffer failures, 0 output buffers swapped out

R3#

3、对FIFO的参数调节

如果一个接口小于2.048M，那么想要它使能FIFO，需要如下配置；

R1(config-if)#no fair-queue 在接口启用FIFO

show interface e0 查看

FIFO输出队列的缓存中默认只容纳40个包，可以修改。

R1(config-if)#hold-queue 50 out