qos

[carl_townshend]

Hi all, can anyone tell me why we have queues on the switch, do we assign a policy to a queue ? and say can have 8 queues on a certain port thus meaning you can have 8 different policies for that port ? also what is the normal or best way to set it up, ie what are the steps in the switch, is it first setup the filter, add this to a queue, assign a priority to the queue then assign ports, can anyone tell the correct way for this ?

many thanks

[carl_townshend]

can anyone clarify this for me?

thanks

[andrew.butterworth]

Carl, your best bet is to read the documentation on CCO. There is a 'Configuring QoS' section in the documentation for all the more recent Catalyst switches. For example here:

http://www.cisco.com/en/US/docs/switches/lan/catalyst3550/software/release/12.2_25_see/configuration/guide/swqos.html

for the Catalyst 3550.

Andy

[bvsnarayana03]

All packets destined for remote locations after reaching a router are queued, waiting for their turn to be delivered. Default queuing mechanism is FIFO, wherein pkts coming 1st in queue are the ones leaving 1st. This may hamper the performance of some applications which are delay sensitive or mission critical.

Queuing is also refered as Congestion management. Thus there are some queuing tools which provide administrator the ability to reorder packets or separate them in to different queues for efficient performance. These methods are generally implemented on output queues.

Queuing tools define the number of queues. Each tool can queue pkts based on acl's, interfaces, markings etc. Thus traffic can be classified based on these factors & pkts of similar type can be put in same queues. Each tool has different No. of queues.

Once the queues are formed, policies can be created to service each queue.

Apart from these, there are lot many mechanisms like:

Shaping & Policing

Congestion Avoidance methods

Link Efficiency methods

Its a huge topic. Refer the attached link for detailed help.

http://www.cisco.com/en/US/products/ps6558/products_white_paper0900aecd802b68b1.shtml