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New Member

Priority QoS


1. In absence of congestion on interface , does the queueing works or not, evening bandwitdh & priority command is used ?

2. Can the default traffic classes (other than Priority class) use the unused bandwidth of Priority class any any situation..

policy-map TESTKING

class Management

bandwidth percent 5

set ip dscp af41

class Premium

priority percent 50

set ip dscp ef

class class-default

bandwidth percent 45


set ip dscp default

int s0/0

max-resv band 100

servicepolicy output TESTKING


Gaurav Prakash


Re: Priority QoS

1. No, there is no need for queueing and so, the bandwidth and priority commands do not come into play.

2. Yes. You can assign a bandwidth statement to the default-class but you cannot assign a priority statement. If there is spare bandwidth available, the default class can certainly use it.

Pls do remember to rate posts.


New Member

Re: Priority QoS

Then whats the difference between priority command & bandwidth command. I know many people speak the same thing as u. This is the line from ciscopress BCRAN CCNP EXAM Certf guide



Here is the link plz go through it. Its short..

Please reply after investigation..

Thanks friend


Re: Priority QoS


both commands will create software queues in a router. The software queueing is only involved, if the hardware queue on an interface is full. In other words: unless you overload an interface there is NO software queueing involved at all. This includes "priority" and "bandwidth".

The priority command will create a strict priority queue. This means packets classified into this queue are serviced immediately before all other packets - thus low latency. There is however an upper limit established through a policer that is automatically enabled with the priority command.

The "bandwidth" command will create a software queue, which will be serviced at least with the configured bandwidth.

So in brief with an example:

priority 30 => low latency queue with a policer at 30 kbps

bandwidth 30 => normal queue with a minimum guaranteed bandwidth of 30 kbps

Hope this helps! Please rate all posts.

Regards, Martin

New Member

Re: Priority QoS

Then it looks the lines from CIsco book the link given above is not correct bcoz it says even if interface is not busy "Priority" command reserves the bandwidth.

Do you have any document whcih explains your point

Re: Priority QoS


just one remark: "reserves the bandwidth" does not mean "blocks the bandwidth". It means once the traffic requests the bandwidth, it will get it. However other traffic can use the bandwidth if it is not needed by the priority class.

You might want to read through: "Comparing the bandwidth and priority Commands of a QoS Service Policy" at

Hope this helps! PLease rate all posts!

Reagrds, Martin

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