Table Of Contents
Low Latency Queueing with Priority Percentage Support
Changes to the bandwidth Command
Changes to the priority Command
How These Commands Calculate Bandwidth
Supported Standards, MIBs, and RFCs
Specifying the Bandwidth Percentage
Verifying the Bandwidth Percentage
Specifying the Bandwidth Percentage
Mixing the Units of Bandwidth for Non-Priority Traffic
Low Latency Queueing with Priority Percentage Support
This feature module describes the Low Latency Queueing with Priority Percentage Support feature and includes the following sections:
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Supported Standards, MIBs, and RFCs
Feature Overview
This feature allows you to configure bandwidth as a percentage within low latency queueing (LLQ). Specifically, you can designate a percentage of the bandwidth to be allocated to an entity (such as a physical interface, a shaped ATM permanent virtual circuit (PVC), or a shaped Frame Relay PVC) to which a policy map is attached. Traffic associated with the policy map will then be given priority treatment.
This feature also allows you to specify the percentage of bandwidth to be allocated to non-priority traffic classes.
This feature modifies two existing commands—bandwidth and priority—and this feature provides additional functionality to the way that bandwidth can be allocated using these two commands.
Changes to the bandwidth Command
This feature adds a new keyword to the bandwidth command—remaining percent. The feature also changes the functionality of the existing percent keyword. These changes result in the following commands for bandwidth: bandwidth percent and bandwidth remaining percent.
The bandwidth percent command configures bandwidth as an absolute percentage of the total bandwidth on the interface.
The bandwidth remaining percent command allows you to allocate bandwidth as a relative percentage of the total bandwidth available on the interface. This command allows you to specify the relative percentage of the bandwidth to be allocated to the classes of traffic. For instance, you can specify that 30 percent of the available bandwidth be allocated to class1, and 60 percent of the bandwidth be allocated to class2. Essentially, you are specifying the ratio of the bandwidth to be allocated to the traffic class. In this case, the ratio is 1 to 2 (30 percent allocated to class1 and 60 percent allocated to class2). The sum of the numbers used to indicate this ratio cannot exceed 100 percent. This way, you need not know the total amount of bandwidth available, just the relative percentage you want to allocate for each traffic class.
Each traffic class gets a minimum bandwidth as a relative percentage of the remaining bandwidth. The remaining bandwidth is the bandwidth available after the priority queue, if present, is given its required bandwidth, and after any Resource Reservation Protocol (RSVP) flows are given their requested bandwidth.
Because this is a relative bandwidth allocation, the packets for the traffic classes are given a proportionate weight only, and no admission control is performed to determine whether any bandwidth (in kbps) is actually available. The only error checking that is performed is to ensure that the total bandwidth percentages for the classes do not exceed 100 percent.
For more information about how this feature defines and calculates bandwidth, see the "How These Commands Calculate Bandwidth" section of this document. For the bandwidth command syntax description and usage guidelines, see the "Command Reference" section of this document.
Changes to the priority Command
This feature also adds the percent keyword to the priority command. The priority percent command indicates that the bandwidth will be allocated as a percentage of the total bandwidth of the interface. You can then specify the percentage (that is, a number from 1 to 100) to be allocated by using the percentage argument with the priority percent command.
Unlike the bandwidth command, the priority command provides a strict priority to the traffic class, which ensures low latency to high priority traffic classes.
For more information about how this feature defines and calculates bandwidth, see the "How These Commands Calculate Bandwidth" section of this document. For the priority command syntax description and usage guidelines, see the "Command Reference" section of this document.
How These Commands Calculate Bandwidth
When the bandwidth and priority commands calculate the total amount of bandwidth available on an entity, the following guidelines are invoked:
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For more information on bandwidth allocation, refer to the chapter "Congestion Management Overview" in the Cisco IOS Quality of Service Solutions Configuration Guide, Release 12.2.
Benefits
This feature allows the Cisco IOS software to accommodate networks with a large number of interfaces, all with differing bandwidths. This feature is especially useful when all of those interfaces with differing bandwidths need to be associated with a policy map that allocates proportional bandwidths to multiple classes.
Additionally, configuring bandwidth in percentages is most useful when the underlying link bandwidth is unknown or the relative class bandwidth distributions are known. For interfaces that have adaptive shaping rates (such as available bit rate (ABR) virtual circuits), CBWFQ can be configured by configuring class bandwidths in percentages.
Restrictions
Dropping Excess Traffic
If the incoming high priority traffic exceeds the bandwidth percentage calculated by the priority percent command, and there is congestion in the network, the excess traffic is dropped. This is identical to the behavior demonstrated when the priority command uses bandwidth in kbps. In both cases, if the high priority traffic exceeds the bandwidth, and there is congestion in the network, excess traffic is dropped.
Exceeding the Configured Bandwidth Percentage Calculated by the bandwidth percent and priority percent Commands
By default, when the bandwidth percent and priority percent commands are used to allocate bandwidth, the sum of the bandwidth percentage allocated to the high priority traffic and the bandwidth percentage allocated to the non-priority traffic cannot exceed 75 percent of the total bandwidth available on the interface.
The remaining 25 percent of the total bandwidth available on the interface is kept in reserve for the unclassified traffic and routing traffic, if any, and proportionally divided among the defined traffic classes. To override the 75 percent limitation, use the max-reserved bandwidth command in interface configuration mode.
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Supported Platforms
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Supported Standards, MIBs, and RFCs
Standards
No new or modified standards are supported by this feature.
MIBs
No new or modified MIBs are supported by this feature.
To obtain lists of supported MIBs by platform and Cisco IOS release, and to download MIB modules, go to the Cisco MIB web site on Cisco.com at http://www.cisco.com/public/sw-center/netmgmt/cmtk/mibs.shtml.
RFCs
No new or modified RFCs are supported by this feature.
Configuration Tasks
See the following sections for configuration tasks for the Low Latency Queueing with Priority Percentage Support feature. Each task in the list is identified as either optional or required:
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Specifying the Bandwidth Percentage
To specify the bandwidth percentage, use the following commands beginning in global configuration mode:
Verifying the Bandwidth Percentage
To display the contents of a policy map and to verify that the percentage has been configured as specified, use the following commands in EXEC mode, as needed:
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Configuration Examples
This section provides the following configuration examples:
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Specifying the Bandwidth Percentage
The following example uses the priority percent command to specify a bandwidth percentage of 10 percent for the class called voice-percent. Then the bandwidth remaining percent command is used to specify a bandwidth percentage of 30 percent for the class called data1, and a bandwidth percentage of 20 percent for the class called data2:
policy-map policy1class voice-percentpriority percent 10class data1bandwidth remaining percent 30class data2bandwidth remaining percent 20As a result of this configuration, 10 percent of the interface bandwidth is guaranteed for the class called voice-percent. The classes called data1 and data2 get 30 percent and 20 percent of the remaining bandwidth, respectively.
Mixing the Units of Bandwidth for Non-Priority Traffic
If a particular unit (that is, kbps or percentages) is used when specifying the bandwidth for a specific class of non-priority traffic, the same bandwidth unit must be used when specifying the bandwidth for the other non-priority classes in that policy map. The bandwidth units within the same policy map must be identical. However, the unit for the priority command in the priority class can be different from the bandwidth unit of the non-priority class. The same configuration can contain multiple policy maps, however, which in turn can use different bandwidth units.
The following sample configuration contains three policy maps—policy1, policy2, and policy3. In the policy map called policy1 and the policy map called policy2, the bandwidth is specified by percentage. However, in the policy map called policy3, bandwidth is specified in kbps.
policy-map policy1class voice-percentpriority percent 10class data1bandwidth percent 30class data2bandwidth percent 20policy-map policy2class voice-percentpriority percent 10class data1bandwidth remaining percent 30class data2bandwidth remaining percent 20policy-map policy3class voice-percentpriority percent 500class data1bandwidth 30class data2bandwidth 20Command Reference
This section documents modified commands. All other commands used with this feature are documented in the Cisco IOS Quality of Service Solutions Command Reference, Release 12.2.
bandwidth (policy-map class)
To specify or modify the bandwidth allocated for a class belonging to a policy map, use the bandwidth command in policy-map class configuration mode. To remove the bandwidth specified for a class, use the no form of this command.
bandwidth {bandwidth-kbps | remaining percent percentage | percent percentage}
no bandwidth {bandwidth-kbps | remaining percent percentage | percent percentage}
Syntax Description
Defaults
This command has no default behavior or values.
Command Modes
Policy-map class configuration
Command History
Usage Guidelines
You should use the bandwidth command when you configure a policy map for a class defined by the class-map command. The bandwidth command specifies the bandwidth for traffic in that class. Class-based weighted fair queueing (CBWFQ) derives the weight for packets belonging to the class from the bandwidth allocated to the class. CBWFQ then uses the weight to ensure that the queue for the class is serviced fairly.
Besides specifying the amount of bandwidth in kbps, you can specify bandwidth as a percentage of either the available bandwidth or the total bandwidth. During periods of congestion, the classes are serviced in proportion to their configured bandwidth percentages. Available bandwidth is equal to the interface bandwidth minus the sum of all bandwidths reserved by the Resource Reservation Protocol (RSVP) feature, the IP RTP Priority feature, and the Low Latency Queueing (LLQ) feature. For a definition of total bandwidth and how it is calculated, see the "How These Commands Calculate Bandwidth" section earlier in this document.
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The following restrictions apply to the bandwidth command:
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For more information on bandwidth allocation, refer to the chapter "Congestion Management Overview" in the Cisco IOS Quality of Service Solutions Configuration Guide, Release 12.2.
Examples
CBWFQ Bandwidth Guarantee Example
The following example illustrates how bandwidth is guaranteed when only CBWFQ is configured:
! The following commands create a policy map with two classes:policy-map policy1class class1bandwidth percent 50exitclass class2bandwidth percent 25exitend!The following commands attach the policy to interface s3/2:interface s3/2service output policy1endThe following output from the show policy-map command shows the configuration for the policy map called policy1:
Router# show policy-map policy1Policy Map policy1Class class1Weighted Fair QueueingBandwidth 50 (%) Max Threshold 64 (packets)Class class2Weighted Fair QueueingBandwidth 25 (%) Max Threshold 64 (packets)The output from the show policy-map interface command shows that 50 percent of the interface bandwidth is guaranteed for the class called class1, and 25 percent is guaranteed for the class called class2. The output displays the amount of bandwidth as both a percentage and a number of kbps.
Router# show policy-map interface s3/2Serial3/2Service-policy output:policy1Class-map:class1 (match-all)0 packets, 0 bytes5 minute offered rate 0 bps, drop rate 0 bpsMatch:noneWeighted Fair QueueingOutput Queue:Conversation 265Bandwidth 50 (%)Bandwidth 772 (kbps) Max Threshold 64 (packets)(pkts matched/bytes matched) 0/0(depth/total drops/no-buffer drops) 0/0/0Class-map:class2 (match-all)0 packets, 0 bytes5 minute offered rate 0 bps, drop rate 0 bpsMatch:noneWeighted Fair QueueingOutput Queue:Conversation 266Bandwidth 25 (%)Bandwidth 386 (kbps) Max Threshold 64 (packets)(pkts matched/bytes matched) 0/0(depth/total drops/no-buffer drops) 0/0/0Class-map:class-default (match-any)0 packets, 0 bytes5 minute offered rate 0 bps, drop rate 0 bpsMatch:anyIn this example, interface s3/2 has a total bandwidth of 1544 kbps. During periods of congestion, 50 percent (or 772 kbps) of the bandwidth is guaranteed to the class called class1, and 25 percent (or 386 kbps) of the link bandwidth is guaranteed to the class called class2.
CBWFQ and LLQ Bandwidth Allocation Example
The following output from the show policy-map command shows the configuration for a policy map called p1:
Router# show policy-map p1Policy Map p1Class voiceWeighted Fair QueueingStrict PriorityBandwidth 500 (kbps) Burst 12500 (Bytes)Class class1Weighted Fair QueueingBandwidth remaining 50 (%) Max Threshold 64 (packets)Class class2Weighted Fair QueueingBandwidth remaining 25 (%) Max Threshold 64 (packets)The following output from the show policy-map interface command on serial interface 3/2 shows that 500 kbps of bandwidth is guaranteed for the class called voice1. The classes called class1 and class2 receive 50 percent and 25 percent of the remaining bandwidth, respectively. Any unallocated bandwidth is divided proportionally among class1, class2, and any best-effort traffic classes.
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Router# show policy-map interface s3/2Serial3/2Service-policy output:p1Class-map:voice (match-all)0 packets, 0 bytes5 minute offered rate 0 bps, drop rate 0 bpsMatch:ip precedence 5Weighted Fair QueueingStrict PriorityOutput Queue:Conversation 264Bandwidth 500 (kbps) Burst 12500 (Bytes)(pkts matched/bytes matched) 0/0(total drops/bytes drops) 0/0Class-map:class1 (match-all)0 packets, 0 bytes5 minute offered rate 0 bps, drop rate 0 bpsMatch:noneWeighted Fair QueueingOutput Queue:Conversation 265Bandwidth remaining 50 (%) Max Threshold 64 (packets)(pkts matched/bytes matched) 0/0(depth/total drops/no-buffer drops) 0/0/0Class-map:class2 (match-all)0 packets, 0 bytes5 minute offered rate 0 bps, drop rate 0 bpsMatch:noneWeighted Fair QueueingOutput Queue:Conversation 266Bandwidth remaining 25 (%) Max Threshold 64 (packets)(pkts matched/bytes matched) 0/0(depth/total drops/no-buffer drops) 0/0/0Class-map:class-default (match-any)0 packets, 0 bytes5 minute offered rate 0 bps, drop rate 0 bpsMatch:anyRelated Commands
priority
To give priority to a class of traffic belonging to a policy map, use the priority command in policy-map class configuration mode. To remove a previously specified priority for a class, use the no form of this command.
priority {bandwidth-kbps | percent percentage} [burst]
no priority {bandwidth-kbps | percent percentage} [burst]
Syntax Description
Defaults
This command has no default behavior or values.
Command Modes
Policy-map class configuration
Command History
Usage Guidelines
This command configures low latency queueing (LLQ), providing strict priority queueing (PQ) for class-based weighted fair queueing (CBWFQ). Strict PQ allows delay-sensitive data such as voice to be dequeued and sent before packets in other queues are dequeued.
The priority command allows you to set up classes based on a variety of criteria (not just User Datagram Ports (UDP) ports) and assign priority to them, and is available for use on serial interfaces and ATM permanent virtual circuits (PVCs). A similar command, the ip rtp priority command, allows you to stipulate priority flows based only on UDP port numbers and is not available for ATM PVCs.
When the device is not congested, the priority class traffic is allowed to exceed its allocated bandwidth. When the device is congested, the priority class traffic above the allocated bandwidth is discarded.
The bandwidth and priority commands cannot be used in the same class, within the same policy map. These commands can be used together in the same policy map, however.
Within a policy map, you can give one or more classes priority status. When multiple classes within a single policy map are configured as priority classes, all traffic from these classes is queued to the same, single, priority queue.
When the policy map containing class policy configurations is attached to the interface to stipulate the service policy for that interface, available bandwidth is assessed. If a policy map cannot be attached to a particular interface because of insufficient interface bandwidth, then the policy is removed from all interfaces to which it was successfully attached.
For more information on bandwidth allocation, refer to the chapter "Congestion Management Overview" in the Cisco IOS Quality of Service Solutions Configuration Guide, Release 12.2.
Examples
The following example configures PQ with a guaranteed bandwidth of 50 kbps and a one-time allowable burst size of 60 bytes for the policy map called policy1:
router(config)# policy-map policy1router(config-pmap)# class voicerouter(config-pmap-c)# priority 50 60In the following example, 10 percent of the available bandwidth is reserved for the class called voice on interfaces to which the policy map called policy1 has been attached:
router(config)# policy-map policy1router(config-pmap)# class voicerouter(config-pmap-c)# priority percent 10Related Commands
Guest
