| Step 1—Create an Output Priority Queuing List
A priority list is a set of rules that describe the way packets should be assigned to priority queues. You can establish queuing priorities based on the protocol type or on packets entering from a specific interface.
You can set a priority queue either by protocol type or by incoming interface type.
Create an output PQ list with the
priority-list protocol
command
:
Router(config)#priority-list list-number
protocol protocol-name
{high | medium
| normal | low} queue-keyword keyword-value
You can also create an output PQ list
with the priority-list interface
command. Use this command to set queuing priorities for all traffic
arriving on an incoming interface :
Router(config)#priority-list list-number
interface interface-type
interface-number {high
| medium | normal | low}
Step 2—Assign a Default Queue
You must explicitly assign a queue for packets that were not specified in the priority list.
The default queue is normal. Use the priority-list default
command to assign packets to a queue if no other priority list conditions are met:
Router(config)#priority-list list-number
default
{high | medium | normal | low}
Step 3—Specify the Queue Sizes (optional)
You can specify the maximum number of allowable
packets in each queue. In general, it is recommended that the default
queue sizes not be changed.
Use the optional priority-list
queue-limit command to change the default
maximum number of packets in each queue :
Router(config)#priority-list list-number
queue-limit
high-limit medium-limit normal-limit low-limit
Step 4-Assign the Priority List Number to an
Interface
Only one list can be assigned per interface. When
assigned, the priority list rules are applied to all traffic that passes
through the interface.
After you define the priority list, enter
interface configuration mode, and enter the priority-group
command to link a priority list to an interface :
Router(config-if)#priority-group
list
In the configuration shown in Figure ,
priority-list 2
specifies the following:
- Telnet (TCP port 23) traffic is assigned to the high-priority queue.
- Traffic from source network 131.108.0.0 is assigned to the high-priority queue, as specified by access-list 1.
- The list 1 argument in the second line of the configuration specifies that access-list 1 be used to sort packets for placement in the high-priority queue.
- All traffic arriving from Ethernet interface 0 is assigned to the medium-priority queue.
- All other IP traffic is assigned to the normal-priority queue.
- All other traffic not specified in priority-list 2 is assigned to the low-priority queue.
- Queue-size limits have been changed from the default values to the following:
- 15 datagrams for the high queue
- 20 datagrams for the medium queue
- 20 datagrams for the normal queue
- 30 datagrams for the low queue
Notice in Figure
that priority-list 2 is linked to interface serial 0 by the
priority-group 2
command.
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Lab
Activity |
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Our
company has given us the task of connecting
our east coast office with the west coast
office via ISDN. It has been determined that
we need to have a strict queuing policy for
traffic going across this link. Certain
traffic should have a higher priority than
other traffic. We have decided that all TCP
traffic should have high priority, ICMP
traffic should have medium priority, all UDP
traffic should have low priority, and all
other traffic should have normal priority. It
is our responsibility to connect these two
routers together and configure priority
queuing correctly. |
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