c2900XL and QoS (CoS)

Unanswered Question
Mar 24th, 2008


I have a cisco 2924xl with the latest IOS for that model.

I have connected a IP Phone with CoS f 5 enabled on the phone.

Does this switch model support trusting of CoS from the incoming traffic?

If so, how do i set it up?


I have this problem too.
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glen.grant Mon, 03/24/2008 - 05:27

That switch is ancient and EOL , I doubt a switch from that era supported any of those type parameters.

rsabapathee Mon, 03/24/2008 - 21:42

The commnand 'switchport priority extend trust' is also valid on a 802.1q trunk port.

What is the logic behind this?? What is the point of enabling this command on a trunk port?

Jon Marshall Tue, 03/25/2008 - 00:35


Actually it's the other way around. If you are trusting CoS markings then they will only be present on a 802.1q trunk port because the 802.1p CoS markings are contained within the 802.1q vlan tag. That's why when you connect a phone + pc to a switchport that switchport is configured as a trunk.


rsabapathee Wed, 03/26/2008 - 21:17

OK. So its the trunk port which takes notice of the CoS marking.

1. So I only need to enable this command on trunk ports??

2. I connect an IP Phone on fa0/1. PC is connect to Fa2 of IP Phone. Both are on native vlan. The phone has in-built capability to do CoS marking.

Do I need to enable CoS on fa0/1 or on the trunk port which carries the traffic to the next switch?

3. Cisco switch A on port fa0/1 is connected to Cisco switch B on port fa0/24.

Devices connected to switch A do CoS marking.

On which ports do I need to issue the command 'switchport priority trust cos' for the traffic from the specified devices to be given priority.

thx for the clarification.

rsabapathee Thu, 03/27/2008 - 10:57

4. If all traffic are on native vlan. A non-Cisco IP Phone connected to the switch (fa0/1) does CoS marking.

Is the traffic from the device given priority at the egress of the trunk port (to another switch) or at the egress of the fa0/port?

I hope the experts can clarify my ambuigity.


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