Priority Queueing (PQ) On Cisco Routers
A Cisco Certification Exam Review
By Chris Bryant, CCIE #12933
Configuring PQ on a Cisco router is a five-step process. As with several other queueing methods, we use access lists to define the traffic that will be subject to PQ.
R3(config)#access-list 174 permit ip 20.1.1.0 0.0.0.255 30.3.3.0 0.0.0.31
Use the priority-list command to define the queues in which the traffic matching these access lists will be placed.
R3(config)#priority-list 1 protocol ip high ?
fragments Prioritize fragmented IP packets
gt Prioritize packets greater than a specified size
list To specify an access list
lt Prioritize packets less than a specified size
tcp Prioritize TCP packets 'to' or 'from' the specified port
udp Prioritize UDP packets 'to' or 'from' the specified port
<cr>
R3(config)#priority-list 1 protocol ip high list 174
R3(config)#priority-list 1 protocol ip medium tcp 53
The priority-list command can also be used to place traffic into queues according to the interface rather than an access list.
R3(config)#priority-list 1 ?
default Set priority queue for unspecified datagrams
interface Establish priorities for packets from a named interface
protocol priority queueing by protocol
queue-limit Set queue limits for priority queues
R3(config)#priority-list 1 interface ?
Ethernet IEEE 802.3
Null Null interface
Serial Serial
R3(config)#priority-list 1 interface ethernet0 ?
high
medium
normal
low
R3(config)#priority-list 1 interface ethernet0 normal ?
<cr>
R3(config)#priority-list 1 interface ethernet0 normal
If desired, use the priority-list command to change the size of the queues.
R3(config)#priority-list 1 queue-limit ?
<0-32767> High limit
R3(config)#priority-list 1 queue-limit 40 ?
<0-32767> Medium limit
R3(config)#priority-list 1 queue-limit 40 80 ?
<0-32767> Normal limit
R3(config)#priority-list 1 queue-limit 40 80 120 ?
<0-32767> Lower limit
R3(config)#priority-list 1 queue-limit 40 80 120 160
Apply the PQ configuration to an interface with the priority-group command.
R3(config)#interface serial0
R3(config-if)#priority-group 1
Verify with show queueing priority.
R3#show queueing priority
Current priority queue configuration:
List Queue Args
1 high protocol ip list 174
1 medium protocol ip tcp port domain
1 normal interface Ethernet0
1 high limit 40
1 medium limit 80
1 normal limit 120
1 low limit 160
To your success,
Chris Bryant
CCIE #12933
chris@thebryantadvantage.com
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