Do I really need QoS?

[William Reed]

Hey Guys,

I manage a Cisco network with 10x Cat 4506s and 1x Cat4510R all GIG POE. We run Cisco VoIP also.

My question is, do I really need QoS on the switches? We have no WAN sites, this is all on a campus fed by fiber. We have about 400 IP Phones, 500 computers, 100 servers, 100 printers, etc.

Any input or opinions are welcome.

[islam.kamal]

Hi

QOS one of the most important technology which is so important nowdays for traffics which are passed through network.As you mentioned above you have two types of traffic (Data and Voice) , you can do QOS which can help you to classify your traffic and do marking for the traffic , then at any congetion due to any problem on the network by QOS you can drop the least important traffic. The QOS should be done on your Cisco switches globally on the switches and per ports. Please refer to Cisco QOS SRND.

Thank you

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[William Reed]

I have port channels to all my access switches from the core. Do I trust cos or dscp? Also do I enable command on each interface or the port-channel itself?

[islam.kamal]

Hi

for trunks ports , you have to use trust DSCP , under the ports which connected to Cisco phones you have to use trust mls cos.Yes , you have to enable under physical interface. To enable port channel under port channel this is not supported on all devices , only support on cores as ASR , GSR , 6500.

Thank you

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[paolo bevilacqua]

No, as long it is a normally used LAN, you do not need QoS.

[Joseph W. Doherty]

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Posting

Do you really need QoS?  That's an "it depends" answer.

If you have ports which ever congest to the degree it's adverse to the network service requirements of an application, then you may need QoS.  Notice I wrote "may need" because QoS cannot "solve" all congestion issues.  (BTW, there's also a widely held belief that adding bandwidth is the solution to all congestion issues.  Well it can be, but sometimes it can be outrageously more expensive, even on LANs, than using QoS to solve a congestion issue.)

[Wayne DeNardi]

+5 to Joseph's answer above.

If you have no congestion, then no, you don't need QoS, as QoS only comes in to effect when a link is congested.

And then, depending on what other application is causing the congestion, there may be no advantage gained by enabling QoS (ie, if the packets from the other application are similarly marked).

Wayne

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