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QoS in both routers and switches??

1. I've multiple remote sites running 2811 routers with QoS enabled for the serial interfaces. Hanging from the routers are either Catalyst 3550 or 3560 switches. My question is that since the QoS is already enabled in the router, does the QoS need to be enabled and configured in the switches too?

2. I also have a Catalyst 6509 running QoS. Hanging off it are some 3560 switches connected via fiber link. Should QoS also be enabled on the 3560s?

Any real benefits of having QoS enabled in both router and switches...?

Your input is greatly appreciated.




Re: QoS in both routers and switches??

Hie Hieu,

This depends on the purpose you are using QoS for.

If you have a voice setup where say you are using some kind of IP phones or end vocie devices, then it will be a good idea to have end to end QoS for voice traffic.

On the other hand if you are only looking towards data not involving any critical applications, and where you think your 100 Mbps or Gbps LAN will never face congestion, it might be okay to run QoS only on the slower WAN links

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Re: QoS in both routers and switches??

Hi Anand,

Thanks very much for your response.

I forgot to mention that we're running VoIP in our network with quite a few IP phones and all remote links are point-to-point T1s.

The reason why I am asking about this is that I am trying to troubleshoot our video conference audio/video quality issue. We use a Polycom unit set at 384kbps and the bandwith for the Video class is 33% (506 kbps). The QoS seems to be working fine as there's no packets dropped from either end of the local and remote routers when the video conference unit is in use, but video and audio are quite choppy at times. The video conference unit is Polycom configured with IP Precedence 4. I've also verified that the config is set the same at the remote unit.

Here's my QoS config in the routers:

class-map match-any Critical-Data2

match protocol citrix

match protocol sqlnet

match protocol sqlserver

match protocol custom-01

match protocol custom-02

match protocol printer

match protocol secure-http

match protocol ntp

match protocol netbios

match protocol custom-03

match protocol custom-04

class-map match-any Network-Control2

match ip dscp cs6

match ip dscp cs2

class-map match-any Interactive-Video2

match ip precedence 4

class-map match-any Call-Signaling2

match ip dscp cs3

class-map match-all Voice2

match ip dscp ef

class-map match-all Scavenger2

match ip dscp cs1


policy-map WAN-EDGE2

class Voice2

priority percent 20

class Call-Signaling2

bandwidth percent 5

class Critical-Data2

set ip dscp af21

bandwidth percent 23

random-detect dscp-based

class Network-Control2

bandwidth percent 5

class Scavenger2

bandwidth percent 1

class Interactive-Video2

priority percent 33

class class-default

bandwidth percent 10

random-detect dscp-based

random-detect dscp 0 36 40

interface Serial0/0/0

ip address

ip nbar protocol-discovery

ip flow egress

no ip mroute-cache

max-reserved-bandwidth 100

service-policy output WAN-EDGE2

Is there something I can do to make the audio/video quality better over the WAN link? Should the QoS be enabled in the switches too?



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