Configuring Priority Queueing

Priority Queueing Configuration Task List

Defining the Priority List

Assigning Packets to Priority Queues

Specifying the Maximum Size of the Priority Queues

Assigning the Priority List to an Interface

Monitoring Priority Queueing Lists

Priority Queueing Configuration Examples

Priority Queueing Based on Protocol Type Example

Priority Queueing Based on Interface Example

Maximum Specified Size of the Priority Queue Example

Priority List Assigned to an Interface Example

Priority Queueing Using Multiple Rules Example

This chapter describes the tasks for configuring priority queueing (PQ) on a router.

For complete conceptual information, see the section "Priority Queueing" in the chapter "Congestion Management Overview" in this book.

For a complete description of the PQ commands in this chapter, refer to the Cisco IOS Quality of Service Solutions Command Reference. To locate documentation of other commands that appear in this chapter, use the command reference master index or search online.

To identify the hardware platform or software image information associated with a feature, use the Feature Navigator on Cisco.com to search for information about the feature or refer to the software release notes for a specific release. For more information, see the "Identifying Supported Platforms" section in the "Using Cisco IOS Software" chapter in this book.

To configure PQ, perform the tasks described in the following sections. The tasks in the first two sections are required; the task in remaining section is optional.

•Defining the Priority List (Required)

•Assigning the Priority List to an Interface (Required)

•Monitoring Priority Queueing Lists (Optional)

See the end of this chapter for the section "Priority Queueing Configuration Examples."

A priority list contains the definitions for a set of priority queues. The priority list specifies which queue a packet will be placed in and, optionally, the maximum length of the different queues.

In order to perform queueing using a priority list, you must assign the list to an interface. The same priority list can be applied to multiple interfaces. Alternatively, you can create many different priority policies to apply to different interfaces.

To define a priority list, perform the tasks described in the following sections. The task in the first section is required; the task in the remaining section is optional.

•Assigning Packets to Priority Queues (Required)

•Specifying the Maximum Size of the Priority Queues (Optional)

Assign packets to priority queues based on the following qualities:

•Protocol type

•Interface where the packets enter the router

You can specify multiple assignment rules. The priority-list commands are read in order of appearance until a matching protocol or interface type is found. When a match is found, the packet is assigned to the appropriate queue and the search ends. Packets that do not match other assignment rules are assigned to the default queue.

To specify which queue to place a packet in, use the following commands in global configuration mode:

Step 1 

Router(config)# priority-list list-number protocol protocol-name {high | medium | normal | low} queue-keyword keyword-value

Establishes queueing priorities based on the protocol type.

Step 2 

Router(config)# priority-list list-number interface interface-type interface-number {high | medium | normal | low}

Establishes queueing priorities for packets entering from a given interface.

Step 3 

Router(config)# priority-list list-number default {high | medium | normal | low}

Assigns a priority queue for those packets that do not match any other rule in the priority list.

All protocols supported by Cisco are allowed. The queue-keyword argument provides additional options including byte count, TCP service and port number assignments, and AppleTalk, IP, IPX, VINES, or XNS access list assignments. Refer to the priority-list protocol command syntax description in the Cisco IOS Quality of Service Solutions Command Reference.

To specify the maximum number of packets allowed in each of the priority queues, use the following command in global configuration mode:

Router(config)# priority-list list-number queue-limit [high-limit [medium-limit [normal-limit [low-limit]]]

Specifies the maximum number of packets allowed in each of the priority queues.

Use the priority-list queue-limit command for each priority list. The default queue limit arguments are listed in Table 10.

Table 10 Default Priority Queue Packet Limits 

high-limit

20

medium-limit

40

normal-limit

60

low-limit

80

You can assign a priority list number to an interface. Only one list can be assigned per interface. To assign a priority group to an interface, use the following commands beginning in global configuration mode:

Step 1 

Router(config)# interface interface-type interface-number

Specifies the interface, and then enters interface configuration mode.

Step 2 

Router(config-if)# priority-group list-number

Assigns a priority list number to the interface.

To display information about the input and output queues, use the following commands in EXEC mode, as needed:

Router# show queue interface-type interface-number

Displays the contents of packets inside a queue for a particular interface or VC.

Router# show queueing priority

Displays the status of the priority queueing lists.

The following sections provide PQ configuration examples:

•Priority Queueing Based on Protocol Type Example

•Priority Queueing Based on Interface Example

•Maximum Specified Size of the Priority Queue Example

•Priority List Assigned to an Interface Example

•Priority Queueing Using Multiple Rules Example

For information on how to configure PQ, see the section "Priority Queueing Configuration Task List" in this chapter.

The following example establishes queueing based on protocol type. The example assigns 1 as the arbitrary priority list number, specifies IP as the protocol type, and assigns a high priority level to traffic that matches IP access list 10.

The following example establishes queueing based on interface. The example sets any packet type entering on Ethernet interface 0 to a medium priority.

The following example changes the maximum number of packets in the high priority queue to 10. The medium-limit, normal, and low-limit queue sizes remain at their default 40-, 60-, and 80-packet limits.

The following example assigns priority group list 4 to serial interface 0:

Note The priority-group list-number command is not available on ATM interfaces that do not support fancy queueing.

When classifying a packet, the system searches the list of rules specified by priority-list commands for a matching protocol type. The following example specifies four rules:

•DECnet packets with a byte count less than 200 are assigned a medium priority queue level.

•IP packets originating or destined to TCP port 23 are assigned a medium priority queue level.

•IP packets originating or destined to User Datagram Protocol (UDP) port 53 are assigned a medium priority queue level.

•All IP packets are assigned a high priority queue level.

Remember that when using multiple rules for a single protocol, the system reads the priority settings in the order of appearance.