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QOS-4500 12.2.25sg

Sho int cap:

Queuing: rx-(N/A), tx-(1p3q1t, Shaping)

So there are 1 strict prty Q, 3 std Q and 1 Threshold. But in the Interface config, only TX-Queue 3 can be 'priority high'.

Q.1 Why ?

Q.2 Is #3 the 'strict priority Q ?

Q.3 How to assign COS value to Strict prty Q ?

6 REPLIES

Re: QOS-4500 12.2.25sg

Hello,

A.1 because the port ASICS are built this way. In LAN switches generally QoS is very much dependant on the hardware.

A.2 Yes.

A.3 For a configuration example and explanations have a look at

http://www.cisco.com/en/US/products/hw/switches/ps663/products_configuration_guide_chapter09186a00800e47ec.html#67318

In short the command is "qos map dscp to tx-queue ".

Hope this helps! Please rate all posts

Martin

Community Member

Re: QOS-4500 12.2.25sg

Thanks for the answer. A followup. I have nortel I2004 phones connecting to 4500 and these phones are assigning dscp=46 to their packets.

Q.1.Should I 'trust cos' or 'trust dscp' for their ports ?

Q.2. For the same port, when i enter command 'qos trust extend cos 0' for connected PCs, the command doesnot showup in the 'sho run'. How do I be sure its effective ?

Re: QOS-4500 12.2.25sg

Hello,

A.1. you could use both versions in case the settings are correct for 802.1Q CoS bits as well as for DSCP.

A.2. The command "qos trust extend cos 0" can only be used in conjunction with settings for Cisco phones. Basically the Cisco phone will learn through CDP which CoS value to apply to traffic from the PC. I doubt this will work with Nortel phones. You may need to configure the Nortel phones directly and skip this part in the switch config.

Hope this helps! Please rate helpful posts.

Martin

Community Member

Re: QOS-4500 12.2.25sg

Thanks for the prompt reply. Reg. A2 - 'qos trust extend cos 0'. I want to ensure a connected PC is not able to set cos > 0. How to do that if this command doesnot work ??? If the port is 'trust dscp' then a connected PC may exploit it by assigning a high dscp value.

Re: QOS-4500 12.2.25sg

Hello,

your telephone should do this! It is the device which terminates the trunk in case you have a voice and a data VLAN. Check your Nortel IP phone documentation on how to achieve this.

The underlying problem is, that the switch is not able to "know" which ethernet frame comes from the PC and which one comes from the phone.

Hope this helps! Please rate all posts.

Martin

Community Member

Re: QOS-4500 12.2.25sg

Nortel phone doc doesnot talk about COS/DSCP. I got another idea. If on access/data vlan int on 4500, I define 'no trust dscp', then the dscp vlaue passed by PC will be reset to zero (qos vlan-based). Is that correct ?

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