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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 configure PQ, perform the tasks in the following sections. The first two sections are required; the remaining section is 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 in the following sections. The first task is required; the second task is optional.
Assign packets to priority queues based on the following:
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:
| Command | Purpose | |
|---|---|---|
Step 1 | 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 | 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 | 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.
To specify the maximum number of packets allowed in each of the priority queues, use the following command in global configuration mode:
| Command | Purpose |
|---|---|
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 7.
| Priority Queue Argument | 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:
To display information about the input and output queues, use one or more of the following commands in EXEC mode:
| Command | Purpose |
|---|---|
show queue interface-type interface-number | Displays the contents of packets inside a queue for a particular interface or VC. |
show queueing priority | Displays the status of the priority queueing lists. |
The following sections provide PQ configuration examples:
For information on how to configure PQ, see the section "Priority Queueing Configuration Task List" earlier 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.
access-list 10 permit 239.1.1.0 0.0.0.255 priority-list 1 protocol ip high 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.
priority-list 3 interface ethernet 0 medium
The following example changes the maximum number of packets in the high priority queue to 10. The medium-, normal, and low-limit queue sizes remain at their default 40-, 60-, and 80-packet limits.
priority-list 4 queue-limit 10 40 60 80
The following example assigns priority group list 4 to serial interface 0:
interface serial 0 priority-group 4
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:
Remember that when using multiple rules for a single protocol, the system reads the priority settings in the order of appearance.
priority-list 4 protocol decnet medium lt 200 priority-list 4 protocol ip medium tcp 23 priority-list 4 protocol ip medium udp 53 priority-list 4 protocol ip high
Posted: Mon Aug 21 21:32:53 PDT 2000
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