Traffic Management - CCIE Routing and Switching Exam Certification Guide - page 514

Foundation Topics
Queuing Algorithms
A CCIE candidate must be familiar with Cisco router interface queuing methods. Queuing
mechanisms help to prioritize traffic when interfaces become congested. This section covers
FIFO, PQ, CQ, and WFQ.
FIFO
This queuing method does not implement any sophisticated schemes. With FIFO, packets are
sent out in the order that they are received. No prioritization occurs for any traffic. To check an
interface's queuing method, use the show interface command. Next, check the queuing
strategy output. The router output in Example 11-1 shows an Ethernet interface using FIFO.
Example 11-1 Interface Using FIFO Queuing
R4#show interface
Ethernet0 is up, line protocol is up
Hardware is PQUICC Ethernet, address is 0010.7b1b.6f9c (bia 0010.7b1b.6f9c)
MTU 1500 bytes, BW 10000 Kbit, DLY 1000 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation ARPA, loopback not set
ARP type: ARPA, ARP Timeout 04:00:00
Last input 00:00:03, output 00:00:05, output hang never
Last clearing of "show interface" counters never
Queueing strategy: fifo
Output queue 0/40, 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
21536 packets input, 5601684 bytes, 0 no buffer
Received 21536 broadcasts, 0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
0 input packets with dribble condition detected
16262 packets output, 3818070 bytes, 0 underruns
0 output errors, 0 collisions, 1 interface resets
0 babbles, 0 late collision, 1 deferred
0 lost carrier, 0 no carrier
0 output buffer failures, 0 output buffers swapped out
PQ
PQ provides a mechanism to prioritize traffic by using four queues. The four queues are
designated as high, medium, normal, and low, as shown in Figure 11-1. Traffic can be assigned
to the queues based on protocol, port number, or other criteria. As traffic arrives to the router, it