administering cisco qos ip networks - chapter 7

interface custom custom queueing list configuration fair fair queueing configuration priority priority queueing list configuration random-detect random early detection configuration | Ou

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Configuring Queuing and Congestion Avoidance

Solutions in this chapter:

■ Configuring FIFO Queuing

■ Configuring Priority Queuing

■ Configuring Custom Queuing

■ Configuring Weighted Fair Queuing

■ Configuring Random Early Detection

Chapter 7

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Now that we have an understanding of the basic queuing and congestion ance mechanisms, it is time to become familiar with how these mechanisms areconfigured.This chapter describes how to reset an interface to its default queuingmethod, change its queuing method, and configure the queuing methods intro-duced in Chapter 6

avoid-FIFO and weighted fair queuing require very little configuration, whereaspriority and custom queuing configurations can range from extremely simple toquite complex.The level of complexity is almost entirely related to the access liststhat control the functions of the queuing mechanisms, so it is important that youreview access lists in detail before configuring these mechanisms

The configurations shown in this chapter do not represent every possibleconfiguration scenario or configuration option If you need more informationabout configurations not shown in this chapter, there are many excellent exam-ples on Cisco’s Web site (www.cisco.com)

Configuring FIFO Queuing

FIFO is the default queuing mechanism for links with a speed greater than E1(2.048 Mbps) On these links, no special configuration is required However, onlinks of E1 speed or lower, weighted fair queuing is the default queuing mecha-nism.Thus, in order to make FIFO the queuing mechanism for these slowerlinks,WFQ must be manually disabled

Enabling FIFO

The interface command “no fair-queue” is used to disable WFQ when it is thedefault queuing mechanism.The following code disables WFQ so that FIFO canact as the queuing mechanism for that link:

Rosa#show interface serial 0/0

Serial0/0 is up, line protocol is up

Hardware is PowerQUICC Serial Internet address is 192.168.10.1/24 MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec, reliability 255/255, txload 1/255, rxload 1/255 Encapsulation HDLC, loopback not set

Keepalive set (10 sec)

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Last input 00:00:08, output 00:00:00, output hang never

Last clearing of "show interface" counters 5d05h

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

Queueing strategy: weighted fair

Output queue: 0/1000/64/0 (size/max total/threshold/drops)

Conversations 0/2/256 (active/max active/max total)

Reserved Conversations 0/0 (allocated/max allocated)

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

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

51061 packets input, 3102381 bytes, 0 no buffer

Received 51046 broadcasts, 0 runts, 0 giants, 0 throttles

1 input errors, 0 CRC, 1 frame, 0 overrun, 0 ignored, 0 abor

51116 packets output, 3200654 bytes, 0 underruns

0 output errors, 0 collisions, 132 interface resets

0 output buffer failures, 0 output buffers swapped out

Rosa#show interfaces serial 0/0

Hardware is PowerQUICC Serial

Internet address is 192.168.10.1/24

MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec,

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

Encapsulation HDLC, loopback not set

Keepalive set (10 sec)

Last input 00:00:07, output 00:00:08, output hang never

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Last clearing of "show interface" counters 5d05h

Queueing strategy: fifo Output queue 0/40, 0 drops; input queue 0/75, 0 drops

51075 packets input, 3103231 bytes, 0 no buffer Received 51060 broadcasts, 0 runts, 0 giants, 0 throttles

29 carrier transitions DCD=up DSR=up DTR=up RTS=up CTS=up

Verifying FIFO Operations

In order to verify the operation of the FIFO queuing process on an interface, thecommand “show queueing” is used.This command has multiple optional parame-ters to guide IOS in showing only the appropriate information.The output ofthis command shows the status of the FIFO queue along with tail drop statisticsand queue depth:

Rosa#show queueing?

interface custom custom queueing list configuration fair fair queueing configuration

priority priority queueing list configuration random-detect random early detection configuration

| Output modifiers

<cr>

Rosa#show queueing interface serial 0/0

Interface Serial0/0 queueing strategy: fifo

Queueing strategy: fifo Output queue 0/40, 0 drops; input queue 0/75, 0 drops Rosa#

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These results can also be observed in the previous example in the output lowing the “show interface” command.

fol-FIFO with RED

Once FIFO has been successfully configured on an interface, it is possible to addrandom early detection as a congestion avoidance mechanism on that interface

Since RED is not a queuing or traffic prioritization process, it can work in junction with FIFO.The following code activates RED on an interface alreadyconfigured with FIFO.The configuration of RED is explained in further detaillater in this chapter

con-Rosa#configure terminal

Enter configuration commands, one per line End with CNTL/Z.

Rosa(config)#interface serial 0/0 Rosa(config-if)#random-detect Rosa(config-if)#end

Rosa#show interface serial 0/0

Serial0/0 is up, line protocol is up Hardware is PowerQUICC Serial Internet address is 192.168.10.1/24 MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec, reliability 255/255, txload 1/255, rxload 1/255 Encapsulation HDLC, loopback not set

Keepalive set (10 sec) Last input 00:00:06, output 00:00:09, output hang never Last clearing of "show interface" counters 5d06h

Queueing strategy: random early detection(RED)

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Rosa#

Configuring Priority Queuing

The tasks involved in configuring priority queuing are as follows:

■ Define a priority list

■ Assign the priority list to an interface

Of the two tasks, defining the priority list is the most important because it is

at this point that the packet classification is determined for the entire priorityqueuing process.The following discussion includes multiple ways to classify net-work traffic, which will help you apply the principles of priority queuing in yournetwork

Enabling Priority Queuing

The first step in configuring priority queuing is to define the priority list.Thefollowing code depicts the priority-list command and its parameters:

queue-limit Set queue limits for priority queues

The command first requires us to select a priority list number between 1 and16.This is necessary because multiple priority lists can be configured on a singlerouter to control different interfaces using different priority queuing policies.Next, the command requires us to select what we want to prioritize.We can pri-oritize by inbound interface or by protocol type.The command also allows us toselect the default priority of unclassified traffic and to set the queue limits inpackets

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Consider the following sample requirements All packets that enter the routerfrom interface Ethernet 0/0 should be classified as medium priority.The defaultpriority of all unclassified packets should be low AppleTalk traffic should havepriority over all other traffic, so we should assign it to the high priority queue.

TCP/IP traffic should be placed in the normal queue.The code to set up thisconfiguration is as follows:

Rosa#configure terminal

Rosa(config)#priority-list 1 protocol appletalk high

Rosa(config)#priority-list 1 interface ethernet 0/0 medium

Rosa(config)#priority-list 1 protocol ip normal

Rosa(config)#priority-list 1 default low

to configure your priority list using the protocol parameter, you will find certain protocols may not be listed, depending on the feature set sup- ported by your version of the IOS.

A Closer Look at the Protocol Classification

The sample configuration code above uses general protocol classifications such as

“ip” and “appletalk” to classify traffic into certain priority queues Unlike thedefault and interface priority list parameters, the protocol parameter allows you

to design traffic configurations at an even more granular level using the features

of each protocol, or even to make use of access lists to identify specific packetsfor classification It is important to look at the IP protocol in greater detail, since

it is the most common protocol

Rosa(config)#priority-list 1 protocol ip medium ?

fragments Prioritize fragmented IP packets

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gt Prioritize packets greater than a specified size list To specify an access list

lt Prioritize packets less than a specified size tcp Prioritize TCP packets 'to' or 'from' specified port udp Prioritize UDP packets 'to' or 'from' specified port

It is important to reiterate that the configuration of the classification process is crucial to the proper operation of priority queuing The following code is an example of a priority list configuration that can lead

to queue starvation, causing Telnet to stop functioning across the work.

net-Rosa(config)#priority-list 3 protocol ipx high

Rosa(config)#priority-list 3 protocol ip low eq telnet

The intent of this priority list is to prioritize IPX traffic over Telnet traffic However, although it is not evident in this example, the default value of unclassified protocols is normal priority, and consequently, all traffic other than IPX will have absolute priority over Telnet Since this includes high throughput protocols such as FTP, it is possible that the router would be presented with so many packets in the normal priority queue that it never services the low priority queue where Telnet packets are held.

Classification Process Considerations

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Rosa(config)#priority-list 2 protocol ip high tcp telnet Rosa(config)#priority-list 2 protocol ip high list 101 Rosa(config)#priority-list 2 protocol ip medium gt 1000 Rosa(config)#priority-list 2 interface ethernet 0/0 normal Rosa(config)#priority-list 2 default low

Rosa(config)#access-list 101 permit ip host 10.1.1.1 any Rosa(config)#end

Rosa#

In this example, access list 101 was created to identify source host 10.1.1.1

This access list was then applied to the priority list by using the “list” keyword

Applying Your Priority List to an Interface

The process of configuring priority queuing is similar to the process of definingand applying an access list using the “access-list” and “access-group” commands

First the priority-list is defined, and then the priority-group is applied to theinterface.This second step, applying the priority list to an interface, is accom-plished using the interface command “priority-group.” In this example, we applypriority lists 1 and 2, defined earlier, to interfaces serial 0/0 and 0/1 respectively:

Rosa(config)#interface serial 0/0 Rosa(config-if)#priority-group 1 Rosa(config-if)#exit

Rosa(config)#interface serial 0/1 Rosa(config-if)#priority-group 2 Rosa(config-if)#end

Rosa#

Configuring the Queue Limits

The default queue size values are 20, 40, 60, and 80 packets for the high,medium, normal, and low priority queues, respectively.To modify these default

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values, the queue-limit parameter is used at the global configuration level In thefollowing code output, the high, medium, normal, and low priority queues areadjusted to values of 200, 400, 600, and 800 packets, respectively:

Verifying Your Configuration

As in the case of FIFO, the first step in verifying the priority queuing tion is to determine if the queuing process runs properly on the interface.Thecommand “show interface” is used for this purpose:

configura-Rosa#show interface serial 0/0

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Serial0/0 is up, line protocol is up Hardware is PowerQUICC Serial Internet address is 192.168.10.1/24 MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec, reliability 255/255, txload 1/255, rxload 1/255 Encapsulation HDLC, loopback not set, keepalive set (10 sec) Last input 00:00:04, output 00:00:00, output hang never Last clearing of "show interface" counters never

Queueing strategy: priority-list 1 Output queue (queue priority: size/max/drops):

high: 0/20/0, medium: 0/40/0, normal 0/60/0, low 0/80/0

Rosa#

This command also shows the present state of the queues, as well as the imum size and tail drops for each queue Next, you can verify the configuration

max-of the priority lists using the command “show queueing priority.”

Rosa#show queueing priority

Current priority queue configuration:

List Queue Args

1 low default

1 medium interface Serial0/0

1 high protocol appletalk

1 normal protocol ip

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2 low default

2 normal interface Ethernet0/0

2 high protocol ip tcp port telnet

con-Troubleshooting Priority Queuing

The first step in troubleshooting priority queuing is to examine the state of thequeues and the number of tail drops experienced by each queue In the followingoutput, we can clearly see a problem with the low priority queue:

Rosa#show int

Rosa#show interface serial 0/0

Hardware is PowerQUICC Serial Internet address is 192.168.10.1/24 MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec,

reliability 255/255, txload 229/255, rxload 219/255

Encapsulation HDLC, loopback not set, keepalive set (10 sec) Last input 00:00:00, output 00:00:00, output hang never Last clearing of "show interface" counters never

Input queue: 0/75/0 (size/max/drops); Total output drops: 0 Queueing strategy: priority-list 1

Output queue (queue priority: size/max/drops):

high: 17/20/0, medium: 1/40/0, normal 0/60/0, low 80/80/6933

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Rosa#

This output indicates that the high priority queue is receiving most of thetraffic on a congested link Consequently, there is queue starvation in the lowpriority queue, indicated by the queue being full and having a high number oftail drops It would be advisable to review the priority list of this process

The second step in troubleshooting is to use the powerful “debug” feature

of the Cisco IOS For priority queuing, the syntax of the command is “debugpriority.”

Rosa#debug priority 02:05:38: PQ: Serial0/0: cdp (defaulting) -> low 02:05:38: PQ: Serial0/0 output (Pk size/Q 292/3)

In this output, we see that the router has processed a Cisco DiscoveryProtocol (CDP) packet out of the serial 0/0 interface Since CDP was not specif-ically classified in the configuration of priority list 1, PQ classifies the packetunder the default queue, which was configured to use the low priority queue

This is apparent in the debug output “cdp (defaulting) -> low.”The output alsoshows the size of the packet and the queue number the packet was assigned Inthis case, the CDP packet was 292 bytes long and was assigned to queue number

3 Pinging the next hop router will generate some IP traffic

Rosa#ping 192.168.10.2

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 192.168.10.2, timeout is 2 seconds:

!!!!!

Success rate is 100 percent (5/5), round-trip min/avg/max = 28/30/32 ms Rosa#

02:05:47: PQ: Serial0/0: ip -> normal 02:05:47: PQ: Serial0/0 output (Pk size/Q 104/2)

02:05:47: PQ: Serial0/0: ip -> normal

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02:05:47: PQ: Serial0/0 output (Pk size/Q 104/2)

assigning the 104-byte packets to queue number 2

Configuring Custom Queuing

The tasks involved in configuring custom queuing are as follows:

■ Define a custom queue list

■ Assign the custom queue list to an interface

As with priority queuing, the definition of the custom queue list is vital tothe proper operation of custom queuing.This section examines several examples

of custom queuing and explains the potential pitfalls to be avoided when

preparing a custom queue list

Enabling Custom Queuing

The first task in configuring custom queuing is to declare a valid custom queuelist.This is accomplished using the global configuration command “queue-list.” Aswith priority queuing, custom queue lists are identified using a list number:

Rosa(config)#queue-list 1 ?

default Set custom queue for unspecified datagrams interface Establish priority for packets from an interface lowest-custom Set lowest number of queue to be treated as

custom

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protocol priority queueing by protocol queue Configure parameters for a particular queue stun Establish priorities for stun packets

This code output shows the various parameters used to configure priorities

As with priority queuing, custom queuing can prioritize by inbound interface or

by protocols.The default keyword is used to define the queue that will handle allunclassified traffic

Let us configure a custom queue list to meet the following requirements Alldefault traffic will be assigned to queue 1 All AppleTalk and IPX traffic will beassigned to queue 2 All Telnet traffic will be assigned to queue 3 All traffic fromIPX host 3C.ABCD.ABCD.ABCD is to be assigned to queue 4 All trafficcoming from interface Ethernet 0/0 is to be assigned to queue 5 Finally, allremaining IP traffic will be assigned to queue 6 Unlike priority queuing, thequeue numbers used by custom queuing do not represent assigned priority levels

The following custom queue list configuration meets these requirements:

Rosa(config)#access-list 801 permit 3c.abcd.abcd.abcd -1 Rosa(config)#access-list 801 deny -1

Rosa(config)#queue-list 1 default 1 Rosa(config)#end

Rosa#

The first part of the configuration identifies IPX host 3C.ABCD.ABCD.ABCD with the definition of an access list.This access list is later applied in thecustom queue list to place IPX traffic from that host into custom queue 4 Asshown in this example, the classification of custom queuing traffic can use the

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same level of granularity as priority queuing So far, we have classified variousprotocols and interfaces into six different queues Each of these queues has adefault byte count of 1500 bytes and a default queue depth of 20 packets.Thismeans that the custom queuing process should service an equal number of bytesamong each queue However, this does not always remain true when largerpackets reach the custom queuing process.

Adjusting Byte Counts and Queue Sizes

In order to modify the byte count and queue size of each queue, the “queue”keyword of the queue-list command is used Each queue is individually config-ured In the following example, we change the byte count of queues 1, 2, and 3

to 3000 bytes, and the queue depth of queues 4, 5, and 6 to 60 packets:

Rosa(config)#queue-list 1 queue 1 byte-count 3000

Rosa(config)#queue-list 1 queue 3 limit ?

<0-32767> number of queue entries

Rosa(config)#queue-list 1 queue 4 limit 60

Rosa(config)#end

Rosa#

Applying Your Configuration to an Interface

Once you have successfully configured your custom queue list, the second step is

to apply the list against an interface.The interface command “custom-queue-list”

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