Queuing Mechanisms Objectives

Configuring FIFO Queuing

• Router(config-if)#

• FIFO queuing is enabled by default on all interfaces. that have a default bandwidth of more than 2 Mbps
• Weighted fair queuing is enabled if the bandwidth is less than 2 Mbps.
• Disable WFQ to enable FIFO on interfaces that have less than 2 Mbps of bandwidth.

• no fair-queue

Configuring FIFO Queuing (cont.)

• Router(config-if)#

• FIFO queuing allows a maximum of 40 packets to be stored in the output queue.
• This command can be used to increase or decrease the maximum number of buffered packets.
• A large value can be set to support longer bursts (fewer drops, more buffer usage).
• A small value can be set to prevent bursts (more drops).

• hold-queue out

FIFO Example

• interface Ethernet0/0
• ip address 1.1.1.1 255.0.0.0
• !
• interface Serial0/0
• ip address 2.2.2.2 255.0.0.0
• no fair-queue
• hold-queue 50 out
• !

• The serial interface (A/S) has a default bandwidth of 128 kbps.
• WFQ is the default queuing mechanism, and it has to be disabled to enable FIFO queuing.

• The Ethernet interface has a default bandwidth of 10Mbps.
• FIFO is the default queuing mechanism, and it does not need to be configured.

• Up to 50 frames are allowed to be enqueued before the router will start tail-dropping newly arriving packets.

Monitoring and Troubleshooting FIFO

• Router#

• The command displays information about the selected interface(s).

• Router#show interface Serial0/0 Serial0/0 is up, line protocol is up
• Hardware is PowerQUICC Serial
• Internet address is 1.1.1.1/8
• MTU 1500 bytes, BW 128 Kbit, DLY 20000 usec,
• reliability 255/255, txload 1/255, rxload 1/255
• Encapsulation HDLC, loopback not set
• Keepalive set (10 sec)
• Last input 00:00:02, output 00:00:04, output hang never
• Last clearing of "show interface" counters never
• Queueing strategy: fifo
• Output queue 0/50, 0 drops; input queue 0/75, 0 drops
• 5 minute input rate 0 bits/sec, 0 packets/sec
• 5 minute output rate 0 bits/sec, 0 packets/sec
• …

• The queue is currently empty (0/50).
• There can be a maximum of 50 frames in the queue (0/50).

• FIFO queuing is enabled on an interface with a default bandwidth of 128kbps.

• show interface []