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To specify or modify the maximum number of packets the queue can hold for a class policy configured in a policy map, use the queue-limit policy-map class configuration command. To remove the queue packet limit from a class, use the no form of this command.
queue-limit number-of-packets
Syntax Description
number-of-packets A number in the range 1 to 64 specifying the maximum number of packets that the queue for this class can accumulate.
Defaults
64
Command Modes
Policy-map class configuration
Command History
12.0(5)T This command was introduced.
Release
Modification
Usage Guidelines
Weighted fair queueing (WFQ) creates a queue for every class for which a class map is defined. 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 fair queueing process. When the maximum packet threshold you defined for the class is reached, enqueueing of any further packets to the class queue causes tail drop or, if Weighted Random Early Detection (WRED) is configured for the class policy, packet drop to take effect.
Examples
The following example configures a policy map called policy11 to contain policy for a class called acl203. Policy for this class is set so that the queue reserved for it has a maximum packet limit of 40.
policy-map policy11 class acl203 bandwidth 2000 queue-limit 40
Related Commands
class (policy map) Specifies the name of the class whose policy you want to create or change, and the default class (commonly known as the class-default class) before you configure its policy. policy-map Creates or modifies a policy map that can be attached to one or more interfaces to specify a service policy.
Command
Description
Syntax Description
list-number Number of the queue list. Any number from 1 to 16 that identifies the queue list. queue-number Number of the queue. Any number from 1 to 16. The default number of the queue list is queue number 1.
Defaults
This command is disabled by default.
Command Modes
Global configuration
Command History
10.0 This command was introduced.
Release
Modification
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 the show interfaces command to display the current status of the output queues.
Examples
In the following example, the default queue for list 10 is set to queue number 2:
queue-list 10 default 2
Related Commands
custom-queue-list Assigns a custom queue list to an interface. Establishes queueing priorities on packets entering on an interface. Establishes queueing priority based on the protocol type. Specifies how many bytes the system allows to be delivered from a given queue during a particular cycle. Designates the queue length limit for a queue. show queue Displays the contents of packets inside a queue for a particular interface or VC. show queueing Lists all or selected configured queueing strategies.
Command
Description
Syntax Description
list-number Number of the queue list. Any number from 1 to 16 that identifies the queue list. interface-type Type of the interface. interface-number Number of the interface. queue-number Number of the queue. Any number from 1 to 16.
Defaults
No queueing priorities are established.
Command Modes
Global configuration
Command History
10.0 This command was introduced.
Release
Modification
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.
Examples
In the following example, queue list 4 establishes queueing priorities for packets entering on interface tunnel 3. The queue number assigned is 10.
queue-list 4 interface tunnel 3 10
Related Commands
custom-queue-list Assigns a custom queue list to an interface. Assigns a priority queue for those packets that do not match any other rule in the queue list. Establishes queueing priority based on the protocol type. Specifies how many bytes the system allows to be delivered from a given queue during a particular cycle. Designates the queue length limit for a queue. show queue Displays the contents of packets inside a queue for a particular interface or VC. show queueing Lists all or selected configured queueing strategies.
Command
Description
Syntax Description
list-number Number of the queue list. Any number from 1 to 16. protocol-name Protocol type: aarp, apollo, appletalk, arp, bridge (transparent), clns, clns_es, clns_is, cmns, compressedtcp, decnet, decnet_node, decnet_routerl1, decnet_routerl2, dlsw, ip, ipx, pad, rsrb, stun, vines, xns, and x25. queue-number Number of the queue. Any number from 1 to 16. queue-keyword keyword-value Possible keywords are fragments, gt, list, lt, tcp, and udp. See Table 8 from the priority-list protocol command.
Defaults
No queueing priorities are established.
Command Modes
Global configuration
Command History
10.0 This command was introduced.
Release
Modification
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 stun keywords refer only to direct encapsulation.
Use Table 8, Table 9, and Table 10 from the priority-list protocol command to configure the queueing priorities for your system.
Examples
The following example assigns 1 as the custom queue list, specifies DECnet as the protocol type, and assigns 3 as a queue number to the packets sent on this interface:
queue-list 1 protocol decnet 3
The following example assigns DECnet packets with a size greater than 200 bytes to queue number 2:
queue-list 2 protocol decnet 2 gt 200
The following example assigns DECnet packets with a size less than 200 bytes to queue number 2:
queue-list 4 protocol decnet 2 lt 200
The following example assigns traffic that matches IP access list 10 to queue number 1:
queue-list 1 protocol ip 1 list 10
The following example assigns Telnet packets to queue number 2:
queue-list 4 protocol ip 2 tcp 23
The following example assigns UDP Domain Name Service packets to queue number 2:
queue-list 4 protocol ip 2 udp 53
The following example assigns traffic that matches Ethernet type code access list 201 to queue number 1:
queue-list 1 protocol bridge 1 list 201
Related Commands
custom-queue-list Assigns a custom queue list to an interface. Assigns a priority queue for those packets that do not match any other rule in the queue list. Specifies how many bytes the system allows to be delivered from a given queue during a particular cycle. Designates the queue length limit for a queue. show queue Displays the contents of packets inside a queue for a particular interface or VC. show queueing Lists all or selected configured queueing strategies.
Command
Description
To specify how many bytes the system allows to be delivered from a given queue during a particular cycle, use the queue-list queue byte-count global configuration command. To return the byte count to the default value, use the no form of this command.
queue-list list-number queue queue-number byte-count byte-count-number
Syntax Description
list-number Number of the queue list. Any number from 1 to 16. queue-number Number of the queue. Any number from 1 to 16. byte-count-number The average number of bytes the system allows to be delivered from a given queue during a particular cycle.
Defaults
This command is not enabled by default.
The default byte count is 1500 bytes.
Command Modes
Global configuration
Command History
10.0 This command was introduced.
Release
Modification
Examples
In the following example, queue list 9 establishes the byte count as 1400 for queue number 10:
queue-list 9 queue 10 byte-count 1400
Related Commands
custom-queue-list Assigns a custom queue list to an interface. Assigns a priority queue for those packets that do not match any other rule in the queue list. Establishes queueing priorities on packets entering on an interface. Establishes queueing priority based on the protocol type. Specifies how many bytes the system allows to be delivered from a given queue during a particular cycle. Designates the queue length limit for a queue. show queue Displays the contents of packets inside a queue for a particular interface or VC. show queueing Lists all or selected configured queueing strategies.
Command
Description
Syntax Description
list-number Number of the queue list. Any number from 1 to 16. queue-number Number of the queue. Any number from 1 to 16. limit-number Maximum number of packets that can be enqueued at any time. The range is 0 to 32767 queue entries. A value of 0 means that the queue can be of unlimited size. The default queue length limit is 20 entries.
Defaults
The default queue length limit for a queue is 20.
Command Modes
Global configuration
Command History
10.0 This command was introduced.
Release
Modification
Examples
In the following example, the queue length of queue 10 is increased to 40:
queue-list 5 queue 10 limit 40
Related Commands
custom-queue-list Assigns a custom queue list to an interface. Assigns a priority queue for those packets that do not match any other rule in the queue list. Establishes queueing priorities on packets entering on an interface. Establishes queueing priority based on the protocol type. Specifies how many bytes the system allows to be delivered from a given queue during a particular cycle. show queue Displays the contents of packets inside a queue for a particular interface or VC. show queueing Lists all or selected configured queueing strategies.
Command
Description
To enable Weighted Random Early Detection (WRED) or VIP-Distributed WRED (DWRED), use the random-detect interface configuration command. To configure WRED as class policy in a policy map, use the random-detect policy-map class configuration command. To disable WRED or DWRED, use the no form of this command.
random-detectSyntax Description
This command has no arguments or keywords.
Defaults
WRED and DWRED are disabled by default.
Command Modes
Interface configuration when used on an interface.
Policy-map class configuration when used to specify class policy in a policy map.
Command History
11.1 CC and 11.2 This command was introduced.
Release
Modification
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.
The router automatically determines parameters to use in the WRED calculations. To change these parameters, use the random-detect precedence command.
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.
WRED in a Policy Map
You can configure WRED as part of the policy 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 for class policy. 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 for class policy, tail drop is used.
To configure a policy map and create class policies, use the policy-map and class (policy map) commands. When specifying class policy within a policy map, you can use the random-detect command with either of the following commands:
Note that if you use WRED packet drop instead of tail drop for one or more classes composing a policy map, you must ensure that WRED is not configured for the interface to which you attach that service policy.
The DWRED feature is not supported for class policy.
Examples
The following example configures WRED on the High-Speed Serial Interface (HSSI) 0/0/0 interface:
interface Hssi0/0/0 random-detect
The following example configures the policy map called policy1 to contain policy specification for the class called class1. During times of congestion, WRED packet drop is used instead of tail drop.
! The following commands create the class map called class1: class-map class1 match input-interface FE0/1 ! The following commands define policy1 to contain policy specification for class1: policy-map policy1 class class1 bandwidth 1000 random-detect
Related Commands
Configures the WRED and DWRED exponential weight factor for the average queue size calculation. Enables flow-based WRED. Configures WRED and DWRED parameters for a particular IP Precedence. Configures WRED and DWRED parameters for a particular IP Precedence. show interfaces Displays statistics for all interfaces configured on the router or access server. show queueing Lists all or selected configured queueing strategies. show tech-support rsvp Generates a report of all RSVP-related information.
Command
Description
IP Precedence
To enable per-virtual circuit (VC) Weighted Random Early Detection (WRED) or per-VC VIP-Distributed WRED (DWRED), use the random-detect VC submode command. To disable per-VC WRED and per-VC DWRED, use the no form of this command.
random-detect [attach group-name]
Syntax Description
attach group-name (Optional) The name of the WRED/DWRED group.
Defaults
WRED and DWRED are disabled by default.
Command Modes
VC submode
Command History
12.0(3)T This command was introduced.
Release
Modification
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/DWRED configuration will override the interface-level configuration if WRED/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.
Remember the following guidelines when using the random-detect (per VC) command:
When this command is used to configure an interface-level WRED/DWRED group to include per-VC WRED/DWRED as a drop policy, the configured WRED/DWRED group parameters are inherited under the following conditions:
When an interface-level WRED/DWRED group configuration is removed, per-VC WRED/DWRED parameters are removed from any VC that inherited them from the configured interface-level WRED/DWRED group.
When an interface-level WRED/DWRED group configuration is modified, per-VC WRED/DWRED parameters are modified accordingly if the WRED/DWRED parameters were inherited from the configured interface-level WRED/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.
Examples
The following example configures per-VC WRED for the permanent virtual circuit (PVC) called cisco. Because the attach keyword was not used, WRED uses default parameters.
pvc cisco 46 random-detect
The following example creates a DWRED group called Rome and then applies the parameter group to an ATM PVC:
! The following commands create the DWRED parameter group Rome: random-detect-group Rome precedence rsvp 46 50 10 precedence 1 32 50 10 precedence 2 34 50 10 precedence 3 36 50 10 precedence 4 38 50 10 precedence 5 40 50 10 precedence 6 42 50 10 precedence 7 44 50 10 exit exit ! The following commands create a PVC on an ATM interface and then apply the ! DWRED group Rome to that PVC: interface ATM2/0.23 point-to-point ip address 10.9.23.10 255.255.255.0 no ip mroute-cache pvc vc1 201/201 random-detect attach Rome vbr-nrt 2000 1000 200 encapsulation aal5snap
The following show queueing command displays the current settings for each of the IP Precedences following configuration of per-VC DWRED:
Router# show queueing random-detect interface atm2/0.23 vc 201/201 random-detect group Rome: exponential weight 9 class min-threshold max-threshold mark-probability ---------------------------------------------------------- 0 30 50 1/10 1 32 50 1/10 2 34 50 1/10 3 36 50 1/10 4 38 50 1/10 5 40 50 1/10 6 42 50 1/10 7 44 50 1/10 rsvp 46 50 1/10
Related Commands
class (policy map) Specifies the name of the class whose policy you want to create or change, and the default class (commonly known as the class-default class) before you configure its policy. Configures the WRED and DWRED exponential weight factor for the average queue size calculation. Defines the WRED or DWRED parameter group. Configures WRED and DWRED parameters for a particular IP Precedence. show interfaces Displays the statistical information specific to a serial interface. show queue Displays the contents of packets inside a queue for a particular interface or VC. show queueing Lists all or selected configured queueing strategies.
Command
Description
To configure the Weighted Random Early Detection (WRED) and VIP-Distributed WRED (DWRED) exponential weight factor for the average queue size calculation for the queue, use the random-detect exponential-weighting-constant interface configuration command. To configure the exponential weight factor for the average queue size calculation for the queue reserved for a class, use the random-detect exponential-weighting-constant policy-map class configuration command. To return the value to the default, use the no form of this command.
random-detect exponential-weighting-constant exponent
Syntax Description
exponent Exponent from 1 to 16 used in the average queue size calculation.
Defaults
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.
Command History
11.1 CC This command was introduced. 12.0(5)T This command was made available as a policy-map class configuration command.
Release
Modification
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.
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/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 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.
Examples
The following example configures WRED on an interface with a weight factor of 10:
interface Hssi0/0/0 description 45Mbps to R1 ip address 10.200.14.250 255.255.255.252 random-detect random-detect exponential-weighting-constant 10
The following example configures the policy map policy1 to contain policy specification for the class called class1. During times of congestion, WRED packet drop is used instead of tail drop. The weight factor used for the average queue size calculation for the queue for class1 is 12.
! The following commands create the class map called class1: class-map class1 match input-interface FE0/1 ! The following commands define policy1 to contain policy specification for class1: policy-map policy1 class class1 bandwidth 1000 random-detect random-detect exponential-weighting-constant 12
Related Commands
exponential-weighting-constant Configures the exponential weight factor for the average queue size calculation for a WRED parameter group. precedence (VC bundle) Configures precedence levels for a VC member of a bundle, or for a VC class that can be assigned to a VC bundle. precedence (WRED group) Configures a WRED group for a particular IP Precedence. Enables WRED or DWRED. Enables per-VC WRED or per-VC DWRED. Configures WRED and DWRED parameters for a particular IP Precedence. show policy-map Displays the configuration of all classes comprising the specified service policy map or all classes for all existing policy maps. show queue Displays the contents of packets inside a queue for a particular interface or VC. show queueing Lists all or selected configured queueing strategies.
Command
Description
To enable flow-based Weighted Random Early Detection (WRED), use the random-detect flow interface configuration command. To disable flow-based WRED, use the no form of this command.
random-detect flowSyntax Description
This command has no arguments or keywords.
Defaults
Flow-based WRED is disabled by default.
Command Modes
Interface configuration
Command History
12.0(3)T This command was introduced.
Release
Modification
Usage Guidelines
You must use this command to enable flow-based WRED before you can use the random-detect flow average-depth-factor and random-detect flow count 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.
Examples
The following example enables flow-based WRED on the Serial1 interface:
interface Serial1 random-detect random-detect flow
Related Commands
Enables WRED or DWRED. Configures the WRED and DWRED exponential weight factor for the average queue size calculation. Sets the multiplier to be used in determining the average depth factor for a flow when flow-based WRED is enabled. Sets the flow count for flow-based WRED. Configures WRED and DWRED parameters for a particular IP Precedence. show interfaces Displays the statistical information specific to a serial interface. show queue Displays the contents of packets inside a queue for a particular interface or VC. show queueing Lists all or selected configured queueing strategies.
Command
Description
ip precedence
Syntax Description
scaling-factor The number 2, 4, 8 or 16. The default value is 4.
Defaults
The default average depth factor is 4.
Command Modes
Interface configuration
Command History
12.0(3)T This command was introduced.
Release
Modification
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-detect flow command to enable flow-based WRED for the interface. To configure flow-based WRED, you may also use the random-detect flow count command.
Examples
The following example enables flow-based WRED on the Serial1 interface and sets the scaling factor for the average flow depth to 8:
interface Serial1 random-detect random-detect flow random-detect flow average-depth-factor 8
Related Commands
Enables WRED or DWRED. Configures the WRED and DWRED exponential weight factor for the average queue size calculation. Enables flow-based WRED. Sets the flow count for flow-based WRED. Configures WRED and DWRED parameters for a particular IP Precedence. show interfaces Displays the statistical information specific to a serial interface. show queue Displays the contents of packets inside a queue for a particular interface or VC. show queueing Lists all or selected configured queueing strategies.
Command
Description
Syntax Description
number Specifies a value from 16 to 215 (32768).
Defaults
256
Command Modes
Interface configuration
Command History
12.0(3)T This command was introduced.
Release
Modification
Usage Guidelines
Before you use this command, you must use the random-detect flow command to enable flow-based WRED for the interface.
Examples
The following example enables flow-based WRED on the Serial1 interface and sets the flow threshold constant to 16:
interface Serial1 random-detect random-detect flow random-detect flow count 16
Related Commands
Enables WRED or DWRED. Configures the WRED and DWRED exponential weight factor for the average queue size calculation. Enables flow-based WRED. Configures WRED and DWRED parameters for a particular IP Precedence. show interfaces Displays the statistical information specific to a serial interface. show queue Displays the contents of packets inside a queue for a particular interface or VC. show queueing Lists all or selected configured queueing strategies.
Command
Description
Syntax Description
group-name Name for the WRED/DWRED parameter group.
Defaults
No WRED/DWRED parameter group exists.
Command Modes
Global configuration
Command History
11.1(22)CC This command was introduced.
Release
Modification
Usage Guidelines
WRED is a congestion avoidance mechanism that slows traffic by randomly dropping packets when there is congestion. 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 when the traffic uses protocols such as TCP, that respond to dropped packets by decreasing the transmission rate.
The router automatically determines parameters to use in the WRED calculations. If you want to change these parameters for a group, use the exponential-weighting-constant or precedence command.
Examples
The following example defines the WRED parameter group called sanjose:
random-detect-group sanjose precedence 0 32 256 100 precedence 1 64 256 100 precedence 2 96 256 100 precedence 3 128 256 100 precedence 4 160 256 100 precedence 5 192 256 100 precedence 6 224 256 100 precedence 7 256 256 100
Related Commands
exponential-weighting-constant Configures the exponential weight factor for the average queue size calculation for a WRED parameter group. precedence (WRED group) Configures a WRED group for a particular IP Precedence. Enables per-VC WRED or per-VC DWRED. show queueing Lists all or selected configured queueing strategies. show queueing interface Displays the queueing statistics of an interface or VC.
Command
Description
Syntax Description
precedence IP Precedence number. The value range is 0 to 7 and RSVP. For Cisco 7000 series routers with an RSP7000 interface processor and Cisco 7500 series routers with a VIP2-40 interface processor (VIP2-50 interface processor strongly recommended), the precedence value range is 0 to 7 only; see Table 12. min-threshold Minimum threshold in number of packets. The value range of this argument is 1 to 4096. When the average queue length reaches the minimum threshold, WRED randomly drops some packets with the specified IP Precedence. max-threshold Maximum threshold in number of packets. The value range of this argument is the value of the min-threshold argument to 4096. When the average queue length exceeds the maximum threshold, WRED drops all packets with the specified IP Precedence. mark-prob-denominator Denominator for the fraction of packets dropped when the average queue depth is at the maximum threshold. For example, if the denominator is 512, one out of every 512 packets is dropped when the average queue is at the maximum threshold. The value range is 1 to 65536. The default is 10; one out of every ten packets is dropped at the maximum threshold.
Defaults
For all precedences, the mark-prob-denominator default is 10, and the max-threshold is based on the output buffering capacity and the transmission speed for the interface.
The default min-threshold depends on the precedence. The min-threshold for IP Precedence 0 corresponds to half of the max-threshold. The values for the remaining precedences fall between half the max-threshold and the max-threshold at evenly spaced intervals.
Table 12 lists the default minimum threshold value for each IP Precedence.
| Minimum Threshold Value (Fraction of Maximum Threshold Value) | ||
|---|---|---|
| IP Precedence | WRED | DWRED |
0 | 9/18 | 8/16 |
1 | 10/18 | 9/16 |
2 | 11/18 | 10/16 |
3 | 12/18 | 11/16 |
4 | 13/18 | 12/16 |
5 | 14/18 | 13/16 |
6 | 15/18 | 14/16 |
7 | 16/18 | 15/16 |
RSVP | 17/18 | --- |
Command Modes
Interface configuration when used on an interface.
Policy-map class configuration when used to specify class policy in a policy map.
Command History
11.1 CC This command was introduced.
Release
Modification
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/DWRED to ignore the precedence when determining which packets to drop, enter this command with the same parameters for each precedence. Remember to use reasonable 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 The default WRED/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 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.
|
Note The DWRED feature is not supported in a class policy. |
Examples
The following example enables WRED on the interface and specifies parameters for the different IP Precedences:
interface Hssi0/0/0 description 45Mbps to R1 ip address 10.200.14.250 255.255.255.252 random-detect random-detect precedence 0 32 256 100 random-detect precedence 1 64 256 100 random-detect precedence 2 96 256 100 random-detect precedence 3 120 256 100 random-detect precedence 4 140 256 100 random-detect precedence 5 170 256 100 random-detect precedence 6 290 256 100 random-detect precedence 7 210 256 100 random-detect precedence rsvp 230 256 100
The following example configures policy for a class called acl10 included in the policy map called policy10. Class acl101 has these characteristics: a minimum of 2000 kbps of bandwidth are expected to be delivered to this class in the event of congestion and a weight factor of 10 is used to calculate the average queue size. For congestion avoidance, WRED packet drop is used, not tail drop. IP Precedence is reset for levels 0 through 4.
policy-map policy10 class acl10 bandwidth 2000 random-detect random-detect exponential-weighting-constant 10 random-detect precedence 0 32 256 100 random-detect precedence 1 64 256 100 random-detect precedence 2 96 256 100 random-detect precedence 3 120 256 100 random-detect precedence 4 140 256 100
Related Commands
bandwidth (policy map) Specifies or modifies the bandwidth allocated for a class belonging to a policy map. Enables WRED or DWRED. Enables per-VC WRED or per-VC DWRED. Configures the WRED and DWRED exponential weight factor for the average queue size calculation. show policy-map interface Displays the configuration of classes configured for service policies on the specified interface or PVC. show queue Displays the contents of packets inside a queue for a particular interface or VC. show queueing Lists all or selected configured queueing strategies.
Command
Description
To configure committed access rate (CAR) and Distributed CAR (DCAR) policies, use the rate-limit interface configuration command. To remove the rate limit from the configuration, use the no form of this command.
rate-limit {input | output} [access-group [rate-limit] acl-index] bps burst-normal burst-max conform-action action exceed-action action
Syntax Description
input Applies this CAR traffic policy to packets received on this interface. output Applies this CAR traffic policy to packets sent on this interface. access-group (Optional) Applies this CAR traffic policy to the specified access list. rate-limit (Optional) The access list is a rate-limit access list. acl-index (Optional) Access list number. bps Average rate in bits per second. The value must be in increments of burst-normal Normal burst size in bytes. The minimum value is bps divided by 2000. burst-max Excess burst size in bytes. conform-action Action to take on packets that conform to the rate limit. action Action to take on packets. Specify one of the following keywords: exceed-action Action to take on packets that exceed the rate limit.
8 kbps.
Defaults
CAR and DCAR are disabled on the interface.
Command Modes
Interface configuration
Command History
11.1 CC This command was introduced.
Release
Modification
Usage Guidelines
Use this command to configure your CAR policy on an interface. To specify multiple policies, enter this command once for each policy.
Distributed CAR is only supported on Cisco 7000 series routers with an RSP7000 or Cisco 7500 series routers with 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.
CAR and DCAR can only be used with IP traffic. Non-IP traffic is not rate limited.
CAR and DCAR can be configured on an interface or subinterface. However, CAR and DCAR are not supported on the Fast EtherChannel, tunnel, or PRI interfaces, nor on any interface that does not support Cisco Express Forwarding (CEF).
CEF must be enabled on the interface before you configure CAR or DCAR.
Examples
The following example limits the rate by application:
interface Hssi0/0/0 description 45Mbps to R2 rate-limit input access-group 101 20000000 24000 32000 conform-action set-prec-transmit 5 exceed-action set-prec-transmit 0 rate-limit input access-group 102 10000000 24000 32000 conform-action set-prec-transmit 5 exceed-action drop rate-limit input 8000000 16000 24000 conform-action set-prec-transmit 5 exceed-action drop ip address 10.200.14.250 255.255.255.252 ! access-list 101 permit tcp any any eq www access-list 102 permit tcp any any eq ftp
The following points further clarify the example:
Related Commands
access-list rate-limit Configures an access list for use with CAR policies. show access-lists rate-limit Displays information about rate-limit access lists. show interfaces rate-limit Displays information about CAR for an interface. show ip rsvp installed Displays RSVP-related installed filters and corresponding bandwidth information.
Command
Description
Syntax Description
input Attaches the specified policy map to the input interface or input VC. output Attaches the specified policy map to the output interface or output VC. policy-map The name of a service policy map (created using the policy-map command) to be attached.
Defaults
No service policy is specified.
Command Modes
Global configuration.
VC submode (for a standalone VC).
Bundle-vc configuration (for ATM VC bundle members).
Command History
12.0(5)T This command was introduced.
Release
Modification
Usage Guidelines
You can attach a single policy map to one or more interfaces or one or more VCs to specify the service policy for those interfaces or VCs.
Currently a service policy specifies class-based weighted fair queueing (CBWFQ). The class policies comprising the policy map are then applied to packets that satisfy the class map match criteria for the class.
To successfully attach a policy map to an interface or a VC, the aggregate of the configured minimum bandwidths of the classes comprising the policy map must be less than or equal to 75 percent of the interface bandwidth or the bandwidth allocated to the VC.
Configuring CBWFQ on a physical interface is only possible if the interface is in the default queueing mode. Serial interfaces at E1 (2.048 Mbps) and below use WFQ by default. Other interfaces use FIFO by default. Enabling CBWFQ on a physical interface overrides the default interface queueing method. Enabling CBWFQ on an ATM permanent virtual circuit (PVC) does not override the default queueing method.
Attaching a service policy and enabling CBWFQ on an interface renders ineffective any commands related to fancy queueing such as commands pertaining to fair queueing, custom queueing, priority queueing, and Weighted Random Early Detection (WRED). You can configure these features only after you remove the policy map from the interface.
You can modify a policy map attached to an interface or a VC, changing the bandwidth of any of the classes comprising the map. Bandwidth changes that you make to an attached policy map are effective only if the aggregate of the bandwidth amounts for all classes comprising the policy map, including the modified class bandwidth, less than or equal to 75 percent of the interface bandwidth or the VC bandwidth. If the new aggregate bandwidth amount exceeds 75 percent of the interface bandwidth or VC bandwidth, the policy map is not modified.
Examples
The following example attaches the service policy map called policy9 to the input interface Serial1:
interface Serial1 service-policy input policy9
The following example attaches the service policy map called policy9 to the input PVC called cisco:
pvc cisco 0/34
service-policy input policy9 vbr-nt 5000 3000 500
precedence 4-7
The following example attaches the policy called policy9 to the output interface serial1 to specify the service policy for the interface and enable CBWFQ on it:
interface serial1 service-policy output policy9
The following example attaches the service policy map called policy9 to the output PVC called cisco:
pvc cisco 0/5
service-policy output policy9
vbr-nt 4000 2000 500
precedence 2-3
Related Commands
policy-map Creates or modifies a policy map that can be attached to one or more interfaces to specify a service policy. show policy-map Displays the configuration of all classes comprising the specified service policy map or all classes for all existing policy maps.
Command
Description
To set the precedence value in the IP header, use the set ip precedence route-map configuration command. To leave the precedence value unchanged, use the no form of this command.
set ip precedence [number | name]
Syntax Description
number | name (Optional) A number or name that sets the precedence bits in the IP header. The values for the number argument and the corresponding name argument are listed in Table 13, from least to most important.
Defaults
This command is disabled by default.
Command Modes
Route-map configuration
Command History
11.0 This command was introduced.
Release
Modification
Usage Guidelines
Table 13 lists the values for the number argument and the corresponding name argument for precedence values in the IP header. They are listed from least to most important.
| Number | Name |
0 | routine |
1 | priority |
2 | immediate |
3 | flash |
4 | flash-override |
5 | critical |
6 | internet |
7 | network |
You can set the precedence using either a number or the corresponding name. Once the IP Precedence bits are set, other QoS services such as weighted fair queueing (WFQ) and Weighted Random Early Detection (WRED) then operate on the bit settings.
The network gives priority (or some type of expedited handling) to the marked traffic through the application of WFQ or WRED at points downstream in the network. Typically, you would set IP Precedence at the edge of the network (or administrative domain) and have queueing act on it thereafter. WFQ can speed up handling for high precedence traffic at congestion points. WRED ensures high precedence traffic has lower loss rates than other traffic during times of congestion.
The mapping from keywords such as routine and priority to a precedence value is useful only in some instances. That is, the use of the precedence bit is evolving. You can define the meaning of a precedence value by enabling other features that use the value. In the case of the high-end Internet QoS available from Cisco, IP Precedences can be used to establish classes of service that do not necessarily correspond numerically to better or worse handling in the network.
Use the route-map (IP) global configuration command with match and set route-map configuration commands to define the conditions for redistributing routes from one routing protocol into another, or for policy routing. Each route-map command has an associated list of match and set commands. The match commands specify the match criteria---the conditions under which redistribution or policy routing is allowed for the current route-map command. The set commands specify the set actions---the particular redistribution or policy routing actions to perform if the criteria enforced by the match commands are met. The no route-map command deletes the route map.
The set route-map configuration commands specify the redistribution set actions to be performed when all of a route map's match criteria are met.
Examples
The following example sets the IP Precedence to 5 (critical) for packets that pass the route-map match:
interface serial 0 ip policy route-map texas route-map texas match length 68 128 set ip precedence 5
Related Commands
fair-queue (WFQ) Enables WFQ for an interface. ip policy route-map Identifies a route map to use for policy routing on an interface. Enables WRED or DWRED. Configures CAR and DCAR policies. route-map (IP) Defines the conditions for redistributing routes from one routing protocol into another, or enables policy routing. traffic-shape adaptive Configures a Frame Relay subinterface to estimate the available bandwidth when BECN signals are received. traffic-shape fecn-adapt Replies to messages with the FECN bit (which are set with TEST RESPONSE messages with the BECN bit set). traffic-shape group Enables traffic shaping based on a specific access list for outbound traffic on an interface. traffic-shape rate Enables traffic shaping for outbound traffic on an interface.
Command
Description
Syntax Description
group-id Group ID number in the range 0 to 99.
Defaults
This command is disabled by default. No group ID is specified.
Command Modes
Route-map configuration
Command History
11.1 CC This command was introduced.
Release
Modification
Usage Guidelines
This command allows you to set a group ID in the routing table that can be used later to classify packets into QoS groups based on prefix, autonomous system, and community string. These packets can then be rate limited or weighted fairly in the queue based on the QoS group ID.
To display QoS group information, use the show ip cef command.
Examples
The following example sets the QoS group to 1 for all packets that match community 1. These packets are then rate limited based on the QoS group ID.
configure terminal route-map precedence-map permit 10 match community 1 set ip qos-group 1 interface hssi0/0/0 bgp-policy source qos-group end
Posted: Fri Jun 23 08:46:24 PDT 2000
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