To change the Quality of Service (QoS) policing action from child first, then parent (the default) to parent first, then child, use the qospoliceorderparent-first command in global configuration mode. To disable the parent-first order and restore the default behavior, use the no form of this command.

Syntax Description

This command has no arguments or keywords.

Command Default

If the qospoliceorderparent-firstcommand is not entered, the child policing action is done first, followed by the parent policing action.

Command Modes

Global configuration (#)

Command History

Usage Guidelines

Prior to Cisco IOS Release 15.1(1)S, in a hierarchical policing policy map (a parent policy with policing configured under a class that has a child policy also with policing configured), the parent policing action was done first, followed by the child policing action.

Beginning in Cisco IOS Release 15.1(1)S, the order is reversed. By default, the child policing action is done first, followed by the parent policing action. This change applies only to software dataplane policer implementations (Cisco 7200, Cisco 7301, and Cisco 7600 FlexWAN and SIP200 line cards).

This new behavior improves the results for transmit-and-drop actions because the child policing action occurs first. However, if the parent and child policers are performing conflicting mark-and-transmit actions, the parent mark takes effect rather than the child because the parent action happens last.

Use of the qospoliceorderparent-first command is necessary only if you need to revert to the police order that was in effect prior to Release 15.1(1)S.

To enable quality of service (QoS) preclassification, use the qospre-classify command in interface configuration mode. To disable the QoS preclassification feature, use the no form of this command.

Syntax Description

This command has no arguments or keywords.

Command Default

QoS preclassification is disabled.

Command Modes

Interface configuration (config-if)

Command History

Usage Guidelines

This command is restricted to tunnel interfaces, virtual templates, and crypto maps. The qospre-classify command is unavailable on all other interface types.

You can enable the qospre-classify command for IP packets only.

Note	QoS preclassification is not supported for all fragmented packets. If a packet is fragmented, each fragment might receive different preclassifications.

Related Commands

To specify the Hierarchical Queuing Framework (HQF) shaper-timer interval, use the qos shape-timer command in global configuration mode. To remove the shaper-timer interval setting, and restore the default value, use the no form of this command.

Syntax Description

Command Default

The shaper-timer interval is 4-milliseconds.

Command Modes

        Global configuration (config)
      

Command History

Usage Guidelines

By default, the shaper timer uses an interval of 4 ms; however, on high-speed interfaces this setting can lead to a burst at the line rate every 4 ms until the token bucket is exhausted. If there is a low-end device immediately downstream, then packets can be dropped during every burst. To eliminate the unwanted burst behavior, you can reduce the token bucket replenish time from 4 ms to 1 ms using the qos shape-timer command.

To configure the shape-timer interval, first you use qos shape-timer command to set the shaper-timer interval, then you create a QoS service policy that specifies the average shape rate, and finally you apply that policy to an interface. Once the policy has been applied to an interface, the interval that the shaper uses to replenish the token bucket is decided by the parameter you specified using the qos shape-timer command.

Note	The qos shape-timer command is available on all Integrated Services Routers (ISRs) that do not have a hardware assisted timer.

Related Commands

To configure the number of incoming packets that the Open Shortest Path First (OSPF) process can keep in its queue, use the queue-depth command in router configuration mode. To set the queue depth to its default value, use the no form of the command.

Syntax Description

Command Default

If you do not set a queue size, the OSPF hello process queue depth is unlimited and the OSPF router process (update) queue depth is 200 packets.

Command Modes

Router configuration (config-router)

Command History

Usage Guidelines

All incoming OSPF packets are initially enqueued in the hello queue. OSPF hello packets are processed directly from this queue, while all other OSPF packet types are subsequently enqueued in the update queue.

If you configure a router with many neighbors and a large database, use the queue-depth command to adjust the size of the hello and router queues. Otherwise, packets might be dropped because of queue limits, and OSPF adjacencies may be lost.

Related Commands

To specify or modify the queue limit (size) for a class in bytes, milliseconds (ms), microseconds (us) or packets, use the queue-limit command in QoS policy-map class configuration mode. To remove the queue limit from a class, use the no form of this command.

Syntax Description

Command Default

The default behavior of the queue-limit command for class queues with and without Weighted Random Early Detection (WRED) is as follows:

• Class queues with WRED--The router uses the default queue limit of two times the largest WRED maximum threshold value, rounded to the nearest power of 2.

  Note	For Cisco IOS Release 12.2(16)BX, the router does not round the value to the nearest power of 2.

• Priority queues and class queues without WRED--The router has buffers for up to 50 ms of 256-byte packets at line rate, but not fewer than 32 packets.

Command Modes

QoS policy-map class configuration (config-pmap-c)

Command History

Usage Guidelines

Weighted Fair Queueing

Weighted fair queueing (WFQ) creates a queue for every class for which a class map is defined. Packets that satisfy the match criterion for a class accumulate in the queue reserved for the class until they are sent, which occurs when the queue is serviced by the fair queueing process. When the maximum packet threshold that you defined for the class is reached, enqueueing of any further packets to the class queue causes tail drop or, if WRED is configured for the class policy, packet drop to take effect.

Changes in Cisco IOS Release 15.0(1)S1

Prior to Cisco IOS Release 15.0(1)S1, if no queue limit was configured, the queue limit for the current class was based on the parent values for available buffers and current class allocated bandwidth. In the implicit WRED min/max scenario, thresholds were calculated from the available buffers.

Thresholds were calculated from the available aggregate queue limit for each class. The WRED min/max threshold values would not be adjusted if there was a user-defined queue-limit configuration. The min/max threshold would still be derived from the "visible_bw" value seen by this traffic class. The WRED functionality could fail because of this inconsistent qlimit and min/max threshold calculation.

Beginning in Cisco IOS Release 15.0(1)S1, the queue limit is always calculated from the parent queue limit and allocated bandwidth in the current class. When you use the queue-limit command to explicitly configure the values, these values are used as the definition of the queue limit.

To ensure optimum functionality, use the queue-limit command to configure the proper min/max threshold for each WRED class based on the queue-limit configuration.

Changes in Cisco IOS Release 15.2(2)T

Prior to Cisco IOS Release 15.2(2)T, if the optional unit of measure was not specified, the unit of measure used was packets. Beginning in Cisco IOS Release 15.2(2)T, if the optional unit of measure is not specified, the unit used depends on the platform.

Overriding Queue Limits Set by the bandwidth Command

Use the bandwidth command with the modular quality of service (QoS) CLI) (MQC) to specify the bandwidth for a particular class. When used with MQC, the bandwidth command has a default queue limit for the class. This queue limit can be modified using the queue-limit command, thereby overriding the default set by the bandwidth command.

Note	Using the queue-limit command to modify the default queue limit is especially important for higher-speed interfaces, in order to meet the minimum bandwidth guarantees required by the interface.

Prior to the deployment of the Hierarchical Queueing Framework (HQF), the default maximum queue limit on a subinterface was 512 if no hold queue was configured on the main interface.

As part of HQF, this restriction was removed beginning in Cisco IOS Release 15.0(1)M5. Now the maximum queue limit can be set as high as the hold-queue size on the main interface.

If no hold queue is configured on the main interface, the aggregate queue limit can go up to 1000. If the hold-queue is explicitly configured on the main interface, then the aggregate queue limit can go up to the hold-queue value. There is no limit per subinterface.

The maximum configurable hold-queue value of 4096 was increased to 240,000 for users who want to configure higher aggregate queue-limit values. However, configuring high queue-limit and hold-queue values is not recommended.

Related Commands

To specify the maximum size (in cells, microseconds, or milliseconds) of a queue for a specific traffic class, use the queue-limitatmclp command in policy-map class configuration mode. To remove the queue limit atm cell loss priority (clp) value from a class, use the no form of this command.

Syntax Description

Command Default

No default behavior or values

Command Modes

Policy-map class configuration (config-pmap-c)

Command History

Usage Guidelines

You can use the queue-limitatmclpcommand only with other queuing features, such as weighted fair queuing (WFQ). WFQ creates a queue for every class for which you define a class map. You can apply the policy map that you created with the atm clp based queue-limit command only to ATM interfaces on Cisco 12000 Series Routers.

Use the queue-limitatmclp command only after you have issued the queue-limitcommand using the same traffic class.

Use the noqueue-limit command to remove both the global queue-limit queue-size value and the queue-limit atm clp queue-size value if you configured it.

Packets satisfying the match criteria for a class accumulate in the queue reserved for the class until they are sent, which occurs when the queue is serviced by the weighted fair queuing process. When the defined maximum packet threshold for the class is reached, enqueuing of additional packets to the class queue causes tail drop.

You can specify the CLP queue-limit threshold in cells, milliseconds (ms), or microseconds (us). However, the unit of measure cannot be mixed. For example, if you specify the CLP queue-limit threshold in milliseconds, then you must also specify the global queue-limit threshold in milliseconds.

Note	When you specify the queue-limit threshold as cells, milliseconds, or microseconds, it is internally converted to cells by using the visible bandwidth that is available to the class or the ATM virtual circuit (VC).

Related Commands

To assign a priority queue for those packets that do not match any other rule in the queue list, use the queue-listdefault command in global configuration mode. To restore the default value, use the noform of this command.

Syntax Description

Command Default

Disabled

The default number of the queue list is queue number 1.

Command Modes

Global configuration

Command History

Usage Guidelines

When you use multiple rules, remember that the system reads the queue-list commands in order of appearance. When classifying a packet, the system searches the list of rules specified by queue-list commands for a matching protocol or interface type. When a match is found, the system assigns the packet to the appropriate queue. The system searches the list in the order specified, and the first matching rule terminates the search.

Queue number 0 is a system queue. It is emptied before any of the other queues are processed. The system enqueues high-priority packets, such as keepalives, to this queue.

Use theshowinterfaces command to display the current status of the output queues.

Related Commands

To establish queueing priorities on packets entering on an interface, use thequeue-listinterface command in global configuration mode. To remove an entry from the list, use the no form of this command.

Syntax Description

Command Default

No queueing priorities are established.

Command Modes

Global configuration

Command History

Usage Guidelines

When you use multiple rules, remember that the system reads the queue-list commands in order of appearance. When classifying a packet, the system searches the list of rules specified by queue-list commands for a matching protocol or interface type. When a match is found, the system assigns the packet to the appropriate queue. The list is searched in the order specified, and the first matching rule terminates the search.

Related Commands

To set the lowest number for a queue to be treated as a custom queue, use the queue-listlowest-customcommand in global configuration mode. To restore the default value, use the noform of this command.

Syntax Description

Command Default

The default number of the lowest custom queue is 1.

Command Modes

Global configuration

Command History

Usage Guidelines

All queues from queue 0 to the queue prior to the one specified in the queue-listlowest-custom command use the priority queue. (Queue 0 has the highest priority.)

All queues from the one specified in the queue-listlowest-custom command to queue 16 use a round-robin scheduler.

Use theshowqueueingcustomcommand to display the current custom queue configuration.

Related Commands

To establish queueing priority based upon the protocol type, use the queue-listprotocol command in global configuration mode. To remove an entry from the list, use the noform of this command.

Syntax Description

Command Default

No queueing priorities are established.

Command Modes

Global configuration

Command History

Usage Guidelines

When you use multiple rules for a single protocol, remember that the system reads the queue-list commands in order of appearance. When classifying a packet, the system searches the list of rules specified by queue-list commands for a matching protocol. When a match is found, the system assigns the packet to the appropriate queue. The system searches the list in the order specified, and the first matching rule terminates the search.

The decnet_router-l1 keyword refers to the multicast address for all level 1 routers, which are intra-area routers, and the decnet_router-l2 keyword refers to all level 2 routers, which are interarea routers.

The dlsw,rsrb, and stunkeywords refer only to direct encapsulation.

Use the tables listed in the priority-listprotocol command documention to configure the queueing priorities for your system.

Related Commands

To specify how many bytes the system allows to be delivered from a given queue during a particular cycle , use the queue-listqueuebyte-count command in global configuration mode. To return the byte count to the default value, use the no form of this command.

Syntax Description

Command Default

This command is disabled by default. The default byte count is 1500 bytes.

Command Modes

Global configuration

Command History

Related Commands

To designate the queue length limit for a queue, use the queue-listqueuelimit command in global configuration mode. To return the queue length to the default value, use the no form of this command.

Syntax Description

Command Default

The default queue length limit is 20 entries.

Command Modes

Global configuration

Command History

Related Commands

Note

Effective with Cisco IOS Release 15.0(1)S and Cisco IOS Release 15.1(3)T, the random-detect command is hidden in interface configuration mode. Although this command is still available in Cisco IOS software, the CLI interactive Help does not display it if you enter a question mark at the command line. This command will be completely removed from interface configuration mode in a future release, which means that you will need to use the appropriate replacement command (or sequence of commands). For more information (including a list of replacement commands), see the "Legacy QoS Command Deprecation" feature document in the Cisco IOS Quality of Service Solutions Configuration Guide.

To enable Weighted Random Early Detection (WRED) or distributed WRED (dWRED) on an interface, use the random-detect command in interface configuration mode. To configure WRED for a class in a policy map, use the random-detect command in QoS policy-map class configuration mode. To disable WRED or dWRED, use the no form of this command.

Syntax Description

Command Default

WRED and dWRED are disabled by default.

Command Modes

Interface configuration (config-if)
QoS policy-map class configuration (config-pmap-c)

Command History

Usage Guidelines

Keywords

If you choose not to use either the dscp-based or the prec-based keyword, WRED uses the IP Precedence value (the default method) to calculate the drop probability for the packet.

Availability

The random-detect command is not available at the interface level for Cisco IOS Releases 12.1E or 12.0S. The random-detect command is available in policy-map class configuration mode only for Cisco IOS Releases 12.1E, 12.0S, and later releases.

WRED Functionality

WRED is a congestion avoidance mechanism that slows traffic by randomly dropping packets when congestion exists. dWRED is similar to WRED but uses the Versatile Interface Processor (VIP) instead of the Route Switch Processor (RSP). WRED and dWRED are most useful with protocols such as Transport Control Protocol (TCP) that respond to dropped packets by decreasing the transmission rate.

The router automatically determines parameters to use in the WRED calculations. To change these parameters, use the random-detect precedence command.

Platform Support for dWRED

The dWRED feature is supported only on Cisco 7000 series routers with an RSP7000 card and Cisco 7500 series routers with a VIP2-40 or higher interface processor. A VIP2-50 interface processor is strongly recommended when the aggregate line rate of the port adapters on the VIP is greater than DS3. A VIP2-50 interface processor is required for OC-3 rates.

To use dWRED, distributed Cisco Express Forwarding switching must first be enabled on the interface. For more information on distributed Cisco Express Forwarding, refer to the Cisco IOS Switching Services Configuration Guide and the Cisco IOS Switching Services Command Reference .

WRED in a Policy Map

You can configure WRED as part of the policy map for a standard class or the default class. The WRED random-detect command and the weighted fair queueing (WFQ) queue-limit command are mutually exclusive. If you configure WRED, its packet drop capability is used to manage the queue when packets exceeding the configured maximum count are enqueued. If you configure the WFQ queue-limit command, tail drop is used.

To configure a policy map and create class policies, use the policy-map and class (policy-map) commands. When creating a class within a policy map, you can use the random-detect command with either of the following commands:

• bandwidth (policy-map class)
• fair-queue (class-default)--for the default class only

Note	If you use WRED packet drop instead of tail drop for one or more classes in a policy map, you must ensure that WRED is not configured on the interface to which you attach that policy map.

Note	dWRED is not supported for classes in a policy map.

Two Methods for Calculating the Drop Probability of a Packet

This command includes two optional keywords, dscp-based and prec-based, that determine the method WRED uses to calculate the drop probability of a packet.

Note the following points when deciding which method to instruct WRED to use:

• With the dscp-based keyword, WRED uses the DSCP value (that is, the first six bits of the IP type of service (ToS) byte) to calculate the drop probability.
• With the prec-based keyword, WRED will use the IP Precedence value to calculate the drop probability.
• The dscp-based and prec-based keywords are mutually exclusive.
• If neither argument is specified, WRED uses the IP Precedence value to calculate the drop probability (the default method).

Related Commands

Note

Effective with Cisco IOS Release 15.1(3)T, the random-detect(per VC) command is hidden. Although this command is still available in Cisco IOS software, the CLI interactive Help does not display it if you attempt to view it by entering a question mark at the command line. This command will be completely removed in a future release. For more information, see the "Legacy QoS Command Deprecation" feature document in the Cisco IOS Quality of Service Solutions Configuration Guide.

To enable per-virtual circuit (VC) Weighted Random Early Detection ( WRED) or per-VC VIP-distributed WRED ( DWRED), use the random-detectcommand in VC submode mode. To disable per-VC WRED and per-VC DWRED, use the no form of this command.

Syntax Description

Command Default

WRED and DWRED are disabled by default.

Command Modes

VC submode

Command History

Usage Guidelines

WRED is a congestion avoidance mechanism that slows traffic by randomly dropping packets when congestion exists. DWRED is similar to WRED but uses the Versatile Interface Processor (VIP) instead of the Route Switch Processor (RSP). WRED and DWRED are most useful with protocols like TCP that respond to dropped packets by decreasing the transmission rate.

WRED and DWRED are configurable at the interface and per-VC levels. The VC-level WRED or DWRED configuration will override the interface-level configuration if WRED or DWRED is also configured at the interface level.

Use this command to configure a single ATM VC or a VC that is a member of a bundle.

Note the following points when using the random-detect(per VC) command:

• If you use this command without the optional attach keyword, default WRED or DWRED parameters (such as minimum and maximum thresholds) are used.
• If you use this command with the optional attach keyword, the parameters defined by the specified WRED or DWRED parameter group are used. (WRED or DWRED parameter groups are defined through the random-detect-group command.) If the specified WRED or DWRED group does not exist, the VC is configured with default WRED or DWRED parameters.

When this command is used to configure an interface-level WRED or DWRED group to include per-VC WRED or DWRED as a drop policy, the configured WRED or DWRED group parameters are inherited under the following conditions:

• All existing VCs--including Resource Reservation Protocol (RSVP) switched virtual circuits (SVCs) that are not specifically configured with a VC-level WRED or DWRED group--will inherit the interface-level WRED or DWRED group parameters.
• Except for the VC used for signalling and the Interim Local Management Interface (ILMI) VC, any VCs created after the configuration of an interface-level DWRED group will inherit the parameters.

When an interface-level WRED or DWRED group configuration is removed, per-VC WRED or DWRED parameters are removed from any VC that inherited them from the configured interface-level WRED or DWRED group.

When an interface-level WRED or DWRED group configuration is modified, per-VC WRED or DWRED parameters are modified accordingly if the WRED or DWRED parameters were inherited from the configured interface-level WRED or DWRED group configuration.

This command is only supported on interfaces that are capable of VC-level queueing. The only currently supported interface is the Enhanced ATM port adapter (PA-A3).

The DWRED feature is only supported on Cisco 7000 series routers with an RSP7000 card and Cisco 7500 series routers with a VIP2-40 or greater interface processor. A VIP2-50 interface processor is strongly recommended when the aggregate line rate of the port adapters on the VIP is greater than DS3. A VIP2-50 interface processor is required for OC-3 rates.

To use DWRED, distributed Cisco Express Forwarding (dCEF) switching must first be enabled on the interface. For more information on dCEF, refer to the Cisco IOS Switching Services Configuration Guide and the Cisco IOS Switching Services Command Reference.

Related Commands

To enable aggregate Weighted Random Early Detection (WRED), use the random-detectaggregatecommand in policy-map class configuration mode. To disable aggregate WRED, use the no form of this command.

Syntax Description

Command Default

If no precedence-based or dscp-basedkeyword is specified in the command, the default is precedence-based.

If optional parameters for a default aggregate class are not defined, all subclass values that are not explicitly configured will use plain (non-weighted) RED drop behavior. This is different from standard random-detect configuration where the default is to always use WRED behavior.

Command Modes

Policy-map class configuration

Command History

Usage Guidelines

For ATM interfaces, the Aggregate WRED feature requires that the ATM SPA cards are installed in a Cisco 7600 SIP-200 carrier card or a Cisco 7600 SIP-400 carrier card.

To configure WRED on an ATM interface, you must use the random-detect aggregate commands; the standard random-detect commands are no longer supported on ATM interfaces.

The precedence-based and dscp-based keywords are mutually exclusive. If you do not specify either keyword, precedence-based is the default.

Defining WRED profile parameter values for the default aggregate class is optional. If defined, WRED profile parameters applied to the default aggregate class will be used for all subclasses that have not been explicitly configured. If all possible IP precedence or DSCP values are defined as subclasses, a default specification is unnecessary. If the optional parameters for a default aggregate class are not defined and packets with an unconfigured IP precedence or DSCP value arrive at the interface, plain (non-weighted) RED drop behavior will be used.

Use this command with a random-detectprecedence(aggregate) or random-detectdscp(aggregate) command within a policy map configuration to configure aggregate Weighted Random Early Detection (WRED) parameters for specific IP precedence or DSCP value(s).

After the policy map is defined, the policy map must be attached at the VC level.

Use the showpolicy-mapinterface command to display the statistics for aggregated subclasses.

Related Commands

To enable weighted random early detection (WRED) on the basis of the ATM cell loss priority (CLP) of a packet, use the random-detectatm-clp-based command in policy-map class configuration mode. To disable WRED, use the no form of this command.

Syntax Description

Command Default

When WRED is configured, the default minimum and maximum thresholdsare determined on the basis of output buffering capacity and the transmission speed for the interface.

The default maximum probability denominator is 10.

On the Cisco 10000 series router, the default is disabled.

Command Modes

Policy-map class configuration (config-pmap-c)

Command History

Usage Guidelines

You cannot use the random-detectatm-clp-based command with the random-detectcos-based command in the same HQF configuration. You must use the norandom-detectcos-based command to disable it before you configure the random-detectatm-clp-based command.

Related Commands

To specify the ATM cell loss priority (CLP) value of a packet, the minimum and maximum thresholds, and the maximum probability denominator used for enabling weighted random early detection (WRED), use the random-detect clp command in policy-map class configuration mode. To reset the thresholds and maximum probability denominator to the default values for the specified ATM CLP, use the no form of this command.

Syntax Description

Command Default

The default values for the min-threshold and max-threshold arguments are based on the output buffering capacity and the transmission speed for the interface.

The default for the max-probability-denominator argument is 10; that is, 1 out of every 10 packets is dropped at the maximum threshold.

Command Modes

Policy-map class configuration (config-pmap-c)

Command History

Usage Guidelines

Note the following points when using the random-detect clp command:

• When the average queue length reaches the minimum threshold, WRED randomly drops some packets with the specified IP precedence.
• When the average queue length exceeds the maximum threshold, WRED drops all packets with the specified IP precedence.
• While the range of values for the min-threshold and max-threshold arguments is from 1 to 512000000, the actual values that you can specify depend on the type of random detect you are configuring. For example, the maximum threshold value cannot exceed the queue limit.
• The max-probability-denominator argument is the fraction of packets dropped when the average queue depth is at the maximum threshold. For example, if the denominator is 512, 1 out of every 512 packets is dropped when the average queue is at the maximum threshold.

Related Commands

To enable weighted random early detection (WRED) on the basis of the class of service (CoS) value of a packet, use the random-detectcos-based command in policy-map class configuration mode. To disable WRED, use the no form of this command.

Syntax Description

Command Default

When WRED is configured, the default minimum and maximum thresholds are determined on the basis of output buffering capacity and the transmission speed for the interface.

The default maximum probability denominator is 10.

Command Modes

Policy-map class configuration (config-pmap-c)

Command History

Usage Guidelines

You cannot use the random-detectcos-based command with the random-detectatm-clp-based command in the same HQF configuration. You must use the norandom-detectatm-clp-based command to disable it before you configure the random-detectcos-based command.

Related Commands

To configure the weighted random early detection (WRED) parameters for a discard-class value for a class policy in a policy map, use the random-detectdiscard-class command in policy-map class configuration mode. To disable the discard-class values, use the no form of this command.

Syntax Description

Command Default

For all precedence levels, the max-probability-denominator default is 10 packets; that is, 1 out of every 10 packets is dropped at the maximum threshold.

Command Modes

Policy-map class configuration   (config-pmap-c)

Command History

Usage Guidelines

When you configure the random-detect discard-class command on an interface, packets are given preferential treatment based on the discard class of the packet. Use the random-detect discard-class command to adjust the discard class for different discard-class values.

Note	While the range of values for the min-threshold and max-threshold arguments is from 1 to 512000000, the actual values that you can specify depend on the type of random detect you are configuring. For example, the maximum threshold value cannot exceed the queue limit.

Cisco 10000 Series Router

You must first enable the drop mode using the random-detect discard-class-based command. You can then set the drop probability profile using the random-detect discard-class command.

The table below lists the default drop thresholds for WRED based on differentiated services code point (DSCP), IP precedence, and discard class. The drop probability indicates that the router drops one packet for every 10 packets.

Related Commands

To base weighted random early detection (WRED) on the discard class value of a packet, use the random-detectdiscard-class-based command in policy-map class configuration mode. To disable this feature, use the no form of this command.

Syntax Description

This command has no arguments or keywords.

Command Default

The defaults are router-dependent.

Command Modes

Policy-map class configuration

Command History

Usage Guidelines

Enter this command so that WRED is based on the discard class instead of on the IP precedence field.

Related Commands

Note

Effective with Cisco IOS Release 15.1(3)T, the random-detect dscp command is hidden in interface configuration mode. Although this command is still available in Cisco IOS software, the CLI interactive Help does not display it if you enter a question mark at the command line. This command will be completely removed from interface configuration mode in a future release, which means that you will need to use the appropriate replacement command (or sequence of commands). For more information (including a list of replacement commands), see the "Legacy QoS Command Deprecation" feature document in the Cisco IOS Quality of Service Solutions Configuration Guide.

To change the minimum and maximum packet thresholds for the differentiated services code point (DSCP) value, use the random-detect dscp command in interface or QoS policy-map class configuration mode. To return the minimum and maximum packet thresholds to the default for the DSCP value, use the no form of this command.

Syntax Description

Command Default

The default values for the random-detect dscp command are different on Versatile Interface Processor (VIP)-enabled Cisco 7500 series routers and Catalyst 6000 family switches with a FlexWAN module (dWRED). All other platforms running WRED have another set of default values. For more information about random-detect dscp defaults, see the "Usage Guidelines" section.

Command Modes

Interface configuration  (config-if)
QoS policy-map class configuration  (config-pmap-c)

Command History

Usage Guidelines

Use the random-detect dscp command in conjunction with the random-detect command in interface configuration mode.

The random-detect dscp command is available only if you specified the dscp-based argument when using the random-detect command in interface configuration mode.

Note	The random-detect dscp command is not available at the interface level for Cisco IOS Release 12.1E or Release 12.0S. The random-detect dscp command is available only in QoS policy-map class configuration mode in Cisco IOS Release 12.1E.

Defaults for VIP-Enabled Cisco 7500 Series Routers and Catalyst 6000 Family Switches with a FlexWAN Module

For all IP precedence values, the default mark-probability-denominator is 10, and the max-threshold value is based on the output buffering capacity and the transmission speed of the interface.

The default min-threshold value depends on the IP precedence value. The min-threshold value for IP precedence 0 corresponds to half of the max-threshold value. The values for the remaining IP precedence values fall between half the max-threshold value and the max-threshold value at even intervals.

Note	Although the range of values for the min-threshold and max-threshold arguments is from 1 to 512000000, the actual values that you can specify depend on the type of random detect you are configuring. For example, the maximum threshold value cannot exceed the queue limit.

Unless the maximum and minimum threshold values for the DSCP values are configured by the user, all DSCP values have the same minimum threshold and maximum threshold values as the value specified for precedence 0.

Specifying the DSCP Value

The random-detect dscp command allows you to specify the DSCP value per traffic class. The DSCP value can be a number from 0 to 63, or it can be one of the following keywords: af11, af12, af13, af21, af22, af23, af31, af32, af33, af41, af42, af43, cs1, cs2, cs3, cs4, cs5, cs7, ef, or rsvp.

On a particular traffic class, eight DSCP values can be configured per traffic class. Overall, 29 values can be configured on a traffic class: 8 precedence values, 12 Assured Forwarding (AF) code points, 1 Expedited Forwarding code point, and 8 user-defined DSCP values.

Assured Forwarding Code Points

The AF code points provide a means for a domain to offer four different levels (four different AF classes) of forwarding assurances for IP packets received from other (such as customer) domains. Each one of the four AF classes is allocated a certain amount of forwarding services (buffer space and bandwidth).

Within each AF class, IP packets are marked with one of three possible drop precedence values (binary 2{010}, 4{100}, or 6{110}), which exist as the three lowest bits in the DSCP header. In congested network environments, the drop precedence value of the packet determines the importance of the packet within the AF class. Packets with higher drop precedence values are discarded before packets with lower drop precedence values.

The upper three bits of the DSCP value determine the AF class; the lower three values determine the drop probability.

Expedited Forwarding Code Points

The EF code point is usually used to mark high-priority, time-sensitive data. The EF code point marking is equal to the highest precedence value; therefore, the EF code point is always equal to precedence value 7.

Class Selector Values

The Class Selector (CS) values are equal to IP precedence values (for instance, cs1 is the same as IP precedence 1).

Default Values

The table below lists the default WRED minimum threshold value for each IP precedence value on the distributed platforms.

Defaults for Non-VIP-Enabled Cisco 7500 Series Routers and Catalyst 6000 Family Switches with a FlexWAN Module

All platforms except the VIP-enabled Cisco 7500 series router and the Catalyst 6000 have the default values shown in the table below.

If WRED is using the DSCP value to calculate the drop probability of a packet, all 64 entries of the DSCP table are initialized with the default settings shown in the table below.

Related Commands

To configure aggregate Weighted Random Early Detection (WRED) parameters for specific differentiated services code point (DSCP) value, use the random-detectdscpvalues(aggregate)command in QoS policy-map class configuration mode. To disable configuration of aggregate WRED DSCP values, use the no form of this command.

Syntax Description

Command Default

For all precedence levels, the mark-prob default value is 10 packets.

Command Modes

QoS policy-map class configuration

Command History

Usage Guidelines

For ATM interfaces, the Aggregate WRED feature requires that the ATM SPA cards are installed in a Cisco 7600 SIP-200 carrier card or a Cisco 7600 SIP-400 carrier card.

To configure WRED on an ATM interface, you must use therandom-detectaggregatecommands; the standard random-detect commands are no longer supported on ATM interfaces.

Use this command with a random-detectaggregate command within a policy map configuration.

Repeat this command for each set of DSCP values that share WRED parameters.

After the policy map is defined, the policy map must be attached at the virtual circuit (VC) level.

The set of subclass (DSCP precedence) values defined on a random-detectdscp(aggregate)CLI will be aggregated into a single hardware WRED resource. The statistics for these subclasses will also be aggregated.

Use the showpolicy-mapinterface command to display the statistics for aggregated subclasses.

Cisco 10000 Series Router

For the PRE2, the random-detect command specifies the default profile for the queue. For the PRE3, the aggregate random-detect command is used instead to configure aggregate parameters for WRED. The PRE3 accepts the PRE2 random-detect command as a hidden command.

On the PRE2, accounting for the default profile is per precedence. On the PRE3, accounting and configuration for the default profile is per class map.

On the PRE2, the default threshold is per precedence for a DSCP or precedence value without an explicit threshold configuration. On the PRE3, the default threshold is to have no WRED configured.

On the PRE2, the drop counter for each precedence belonging to the default profile only has a drop count that matches the specific precedence value. Because the PRE2 has a default threshold for the default profile, the CBQOSMIB displays default threshold values. On the PRE3, the drop counter for each precedence belonging to the default profile has the aggregate counter of the default profile and not the individual counter for a specific precedence. The default profile on the PRE3 does not display any default threshold values in the CBQOSMIB if you do not configure any threshold values for the default profile.

DSCP Values

You must enter one or more differentiated service code point (DSCP) values. The command may include any combination of the following:

• numbers (0 to 63) representing differentiated services code point values
• af numbers (for example, af11) identifying specific AF DSCPs
• cs numbers (for example, cs1) identifying specific CS DSCPs
• default --Matches packets with the default DSCP.
• ef --Matches packets with EF DSCP.

For example, if you wanted the DCSP values of 0, 1, 2, 3, 4, 5, 6, or 7 (note that only one of the IP DSCP values must be a successful match criterion, not all of the specified DSCP values), enter the matchdscp01234567 command.

Related Commands

To enable explicit congestion notification (ECN), use the random-detectecncommand in policy-map class configuration mode. To disable ECN, use the no form of this command.

Syntax Description

This command has no arguments or keywords.

Command Default

By default, ECN is disabled.

Command Modes

Policy-map class configuration

Command History

Usage Guidelines

If ECN is enabled, ECN can be used whether Weighted Random Early Detection (WRED) is based on the IP precedence value or the differentiated services code point (DSCP) value.

Related Commands

Note

Effective with Cisco IOS Release 15.0(1)S and Cisco IOS Release 15.1(3)T, the random-detectexponential-weighting-constantcommand is hidden in interface configuration mode. Although this command is still available in Cisco IOS software, the CLI interactive Help does not display it if you attempt to view it by entering a question mark at the command line. This command will be completely removed from interface configuration mode in a future release, which means that you will need to use the appropriate replacement command (or sequence of commands). For more information (including a list of replacement commands), see the "Legacy QoS Command Deprecation" feature document in the Cisco IOS Quality of Service Solutions Configuration Guide.

To configure the Weighted Random Early Detection (WRED) and distributed WRED (DWRED) exponential weight factor for the average queue size calculation for the queue, use the random-detectexponential-weighting-constantcommand in interface configuration mode. To configure the exponential weight factor for the average queue size calculation for the queue reserved for a class, use the random-detectexponential-weighting-constantcommand in policy-map class configuration mode. To return the value to the default, use the no form of this command.

Syntax Description

Command Default

The default exponential weight factor is 9.

Command Modes

Interface configuration when used on an interface
Policy-map class configuration when used to specify class policy in a policy map or when used in the Modular Quality of Service (QoS) Command-Line Interface (CLI) (MQC)

Command History

Usage Guidelines

WRED is a congestion avoidance mechanism that slows traffic by randomly dropping packets when congestion exists. DWRED is similar to WRED but uses the VIP instead of the Route Switch Processor (RSP). WRED and DWRED are most useful with protocols like TCP that respond to dropped packets by decreasing the transmission rate.

Use this command to change the exponent used in the average queue size calculation for the WRED and DWRED services. You can also use this command to configure the exponential weight factor for the average queue size calculation for the queue reserved for a class.

Note	The default WRED or DWRED parameter values are based on the best available data. We recommend that you do not change the parameters from their default values unless you have determined that your applications would benefit from the changed values.

The DWRED feature is not supported for class policy.

The DWRED feature is supported only on Cisco 7000 series routers with an RSP7000 card and Cisco 7500 series routers with a VIP2-40 or greater interface processor. A VIP2-50 interface processor is strongly recommended when the aggregate line rate of the port adapters on the VIP is greater than DS3. A VIP2-50 interface processor is required for OC-3 rates.

To use DWRED, distributed Cisco Express Forwarding (dCEF) switching must first be enabled on the interface. For more information on dCEF, refer to the Cisco IOS IP Switching Configuration Guide and the Cisco IOS IP Switching Command Reference.

Related Commands

Note

Effective with Cisco IOS Release 15.1(3)T, the random-detectflowcommand is hidden. Although this command is still available in Cisco IOS software, the CLI interactive Help does not display it if you attempt to view it by entering a question mark at the command line. This command will be completely removed in a future release. For more information, see the "Legacy QoS Command Deprecation" feature document in the Cisco IOS Quality of Service Solutions Configuration Guide.

To enable flow-based Weighted Random Early Detection ( WRED), use the random-detectflowcommand in interface configuration mode. To disable flow-based WRED, use the no form of this command.

Syntax Description

This command has no arguments or keywords.

Command Default

Flow-based WRED is disabled by default.

Command Modes

Interface configuration

Command History

Usage Guidelines

You must use this command to enable flow-based WRED before you can use the random-detectflowaverage-depth-factor and random-detectflowcount commands to further configure the parameters of flow-based WRED.

Before you can enable flow-based WRED, you must enable and configure WRED. For complete information, refer to the Cisco IOS Quality of Service Solutions Configuration Guide .

Related Commands

Note

Effective with Cisco IOS Release 15.1(3)T, the random-detectflowaverage-depth-factorcommand is hidden. Although this command is still available in Cisco IOS software, the CLI interactive Help does not display it if you attempt to view it by entering a question mark at the command line. This command will be completely removed in a future release. For more information, see the "Legacy QoS Command Deprecation" feature document in the Cisco IOS Quality of Service Solutions Configuration Guide.

To set the multiplier to be used in determining the average depth factor for a flow when flow-based Weighted Random Early Detection (WRED) is enabled, use the random-detectflowaverage-depth-factorcommand in interface configuration mode. To remove the current flow average depth factor value, use the no form of this command.

Syntax Description

Command Default

The default average depth factor is 4.

Command Modes

Interface configuration

Command History

Usage Guidelines

Use this command to specify the scaling factor that flow-based WRED should use in scaling the number of buffers available per flow and in determining the number of packets allowed in the output queue for each active flow. This scaling factor is common to all flows. The outcome of the scaled number of buffers becomes the per-flow limit.

If this command is not used and flow-based WRED is enabled, the average depth scaling factor defaults to 4.

A flow is considered nonadaptive--that is, it takes up too much of the resources--when the average flow depth times the specified multiplier (scaling factor) is less than the depth for the flow, for example:

average-flow-depth * (scaling factor) < flow-depth

Before you use this command, you must use the random-detectflow command to enable flow-based WRED for the interface. To configure flow-based WRED, you may also use the random-detectflowcount command.

Related Commands

Note

Effective with Cisco IOS Release 15.1(3)T, the random-detectflowcountcommand is hidden. Although this command is still available in Cisco IOS software, the CLI interactive Help does not display it if you attempt to view it by entering a question mark at the command line. This command will be completely removed in a future release. For more information, see the "Legacy QoS Command Deprecation" feature document in the Cisco IOS Quality of Service Solutions Configuration Guide.

To set the flow count for flow-based Weighted Random Early Detection (WRED), use the random-detectflowcountcommand in interface configuration mode. To remove the current flow count value, use the no form of this command.

Syntax Description

Command Default

256

Command Modes

Interface configuration

Command History

Usage Guidelines

Before you use this command, you must use the random-detectflow command to enable flow-based WRED for the interface.

Related Commands

Note	Effective with Cisco IOS Release 12.4(20)T, the random-detectprec-basedcommandisreplacedbytherandom-detectprecedence-basedcommand.Seetherandom-detectprecedence-basedcommand formoreinformation.

To base weighted random early detection (WRED) on the precedence value of a packet, use the random-detectprec-based command in policy-map class configuration mode. To disable this feature, use the no form of this command.

Syntax Description

This command has no arguments or keywords.

Command Default

WRED is disabled by default.

Command Modes

Policy-map class configuration (config-pmap-c)

Command History

Usage Guidelines

With the random-detectprec-based command, WRED is based on the IP precedence value of the packet.

Use the random-detectprec-based command before configuring the random-detectprecedence command.

Beginning with Cisco IOS Release 12.4(20)T, use the random-detectprecedence command when you configure a policy map.

Related Commands

Note

Effective with Cisco IOS Release 15.0(1)S and Cisco IOS Release 15.1(3)T, the random-detect precedence command is hidden in interface configuration mode. Although this command is still available in Cisco IOS software, the CLI interactive Help does not display it if you enter a question mark at the command line. This command will be completely removed from interface configuration mode in a future release, which means that you will need to use the appropriate replacement command (or sequence of commands). For more information (including a list of replacement commands), see the "Legacy QoS Command Deprecation" feature document in the Cisco IOS Quality of Service Solutions Configuration Guide.

To configure Weighted Random Early Detection (WRED) and distributed WRED (dWRED) parameters for a particular IP precedence, use the random-detect precedence command in interface configuration mode. To configure WRED parameters for a particular IP precedence for a class policy in a policy map, use the random-detect precedence command in QoS policy-map class configuration mode. To return the values to the default for the precedence, use the no form of this command.

Syntax Description

Command Default

For all precedences, the mark-probability-denominator default value is 10, and the max-threshold value is based on the output buffering capacity and the transmission speed for the interface.

The default min-threshold value depends on the precedence. The min-threshold value for IP precedence 0 corresponds to half of the max-threshold value. The values for the remaining precedences fall between half the max-threshold value and the max-threshold value at evenly spaced intervals. See the table in the "Usage Guidelines" section of this command for a list of the default minimum threshold values for each IP precedence.

Command Modes

Interface configuration (config-if)

QoS policy-map class configuration (config-pmap-c)

Command History

Usage Guidelines

WRED is a congestion avoidance mechanism that slows traffic by randomly dropping packets when congestion exists. dWRED is similar to WRED but uses the Versatile Interface Processor (VIP) instead of the Route Switch Processor (RSP).

When you configure the random-detect command on an interface, packets are given preferential treatment based on the IP precedence of the packet. Use the random-detect precedence command to adjust the treatment for different precedences.

If you want WRED or dWRED to ignore the precedence when determining which packets to drop, enter this command with the same parameters for each precedence. Remember to use appropriate values for the minimum and maximum thresholds.

Note that if you use the random-detect precedence command to adjust the treatment for different precedences within class policy, you must ensure that WRED is not configured for the interface to which you attach that service policy.

Note	Although the range of values for the min-threshold and max-threshold arguments is from 1 to 512000000, the actual values that you can specify depend on the type of random detect you are configuring. For example, the maximum threshold value cannot exceed the queue limit.

The table below lists the default minimum threshold value for each IP precedence.

Note	The default WRED or dWRED parameter values are based on the best available data. We recommend that you do not change the parameters from their default values unless you have determined that your applications would benefit from the changed values.

The dWRED feature is supported only on Cisco 7000 series routers with an RSP7000 card and Cisco 7500 series routers with a VIP2-40 or higher interface processor. A VIP2-50 interface processor is strongly recommended when the aggregate line rate of the port adapters on the VIP is greater than DS3. A VIP2-50 interface processor is required for OC-3 rates.

To use dWRED, distributed Cisco Express Forwarding (dCEF) switching must first be enabled on the interface. For more information on dCEF, refer to the Cisco IOS IP Switching Configuration Guide and the Cisco IOS IP Switching Command Reference.

Note	The dWRED feature is not supported in a class policy.

Related Commands

To configure aggregate Weighted Random Early Detection (WRED) parameters for specific IP precedence value(s), use the random-detectprecedence(aggregate)command in policy-map class configuration mode. To disable configuration of aggregate WRED precedence values, use the no form of this command.

Syntax Description

Cisco 10000 Series Router

For all precedence levels, the mark-prob default is 10 packets.

Command Modes

Policy-map class configuration

Command History

Usage Guidelines

For ATM interfaces, the Aggregate WRED feature requires that the ATM SPA cards are installed in a Cisco 7600 SIP-200 carrier card or a Cisco 7600 SIP-400 carrier card.

To configure WRED on an ATM interface, you must use the random-detect aggregate commands; the standard random-detect commands are no longer supported on ATM interfaces

Use this command with a random-detectaggregate command within a policy map configuration.

Repeat this command for each set of IP precedence values that share WRED parameters.

After the policy map is defined, the policy map must be attached at the VC level.

The set of subclass (IP precedence) values defined on a random-detectprecedence(aggregate)CLI will be aggregated into a single hardware WRED resource. The statistics for these subclasses will also be aggregated.

Use the showpolicy-mapinterface command to display the statistics for aggregated subclasses.

Cisco 10000 Series Router

The table below lists the default drop thresholds for WRED based on DSCP, IP precedence, and discard-class. The drop probability indicates that the router drops one packet for every 10 packets.

For the PRE2, the random-detect command specifies the default profile for the queue. For the PRE3, the aggregate random-detect command is used instead to configure aggregate parameters for WRED. The PRE3 accepts the PRE2 random-detect command as a hidden CLI.

On the PRE2, accounting for the default profile is per precedence. On the PRE3, accounting and configuration for the default profile is per class map.

On the PRE2, the default threshold is per precedence for a DSCP or precedence value without an explicit threshold configuration. On the PRE3, the default threshold is to have no WRED configured.

On the PRE2, the drop counter for each precedence belonging to the default profile only has a drop count that matches the specific precedence value. Because the PRE2 has a default threshold for the default profile, the CBQOSMIB displays default threshold values. On the PRE3, the drop counter for each precedence belonging to the default profile has the aggregate counter of the default profile and not the individual counter for a specific precedence. The default profile on the PRE3 does not display any default threshold values in the CBQOSMIB if you do not configure any threshold values for the default profile.

Related Commands

Note

Effective with Cisco IOS Release 15.0(1)S and Cisco IOS Release 15.1(3)T, the random-detect-groupcommand is hidden. Although this command is still available in Cisco IOS software, the CLI interactive Help does not display it if you attempt to view it by entering a question mark at the command line. This command will be completely removed in a future release. For more information, see the "Legacy QoS Command Deprecation" feature document in the Cisco IOS Quality of Service Solutions Configuration Guide.

To define the Weighted Random Early Detection (WRED) or distributed WRED (DWRED) parameter group, use the random-detect-groupcommand in global configuration mode. To delete the WRED or DWRED parameter group, use the no form of this command.

Syntax Description

Command Default

No WRED or DWRED parameter group exists.

If you choose not to use either the dscp-based or the prec-based keywords, WRED uses the IP Precedence value (the default method) to calculate drop probability for the packet.

Command Modes

Global configuration

Command History