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QoS trust relationship & marking between Access & Core

I'm still in process of understanding fully QoS, the portion i'm still trying to fully understand in my lab is:

I've got an Access switch, using auto qos on the access ports

On my port-channel uplink to Core, for my voice traffic, i'm setting a priority bandwidth, and marking dscp ef, and cos 3

On my Core, i'm trusting the cos value on the port-channel (mls qos trust cos), and ethernet uplinks for my Access switches.

1.  So the way i understand it is, my voice traffic's ethernet frame is now properly marked w/dscp & cos values appropriate

for voice.  The core trusts the cos value coming from my access switch.  Does it trust the dscp values as well, even

though no explicit cmd was applied to auto trust?

2.  What is the best method, if it's a command or a packet sniff, to view that traffic is correct being classified in a class map,

and that the markings do get applied.

3.  My Access switch does not support 'auto qos trust dscp'.  i have 'auto qos trust cos'.  I have a Tandberg video unit, which

can do dscp markings.  Whats are a few options, and pros and cons of ensuring this traffic is correctly marked?

should i mark all traffic from the port with a specific CoS value

or should i classify the video traffic, and manually set a dscp & cos value, and add it to the service-policy on the uplink

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1 REPLY
Cisco Employee

Re: QoS trust relationship & marking between Access & Core

Hi,

See answers inline:

1.  So the way i understand it is, my voice traffic's ethernet frame is now properly marked w/dscp & cos values appropriate

for voice.  The core trusts the cos value coming from my access switch.  Does it trust the dscp values as well, even

though no explicit cmd was applied to auto trust?

The switch only looks at the cos value of the packet and its not look at the dscp value at all.

2.   What is the best method, if it's a command or a packet sniff, to view  that traffic is correct being classified in a class map,

and that the markings do get applied.

Only 3k switches support "show mls qos int gix/y stat" command which will show incoming and outgoing dscp/cos values on an interface but not for a specific traffic.  Packet sniff would be the best idea.

3.  My Access switch does not support 'auto qos trust dscp'.  i have 'auto qos trust cos'.  I have a Tandberg video unit, which

can do dscp markings.  Whats are a few options, and pros and cons of ensuring this traffic is correctly marked?

Can you not trust the interface with "mls qos trust dscp" and "priority-queue" out that should take care of it.

should i mark all traffic from the port with a specific CoS value

or should i classify the video traffic, and manually set a dscp & cos value, and add it to the service-policy on the uplink

All you need to worry about is to trust the interfaces correctly.

Hope that helps.

JayaKrishna

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