QoS on Catalyst 3500 XL

[kooper390]

Hi all!

I'd like to use a Catalyst 3500 for VoIP traffic.

Can I use the QoS feature without any configuration? Just sending ethernet frames with priority?

Deployment:

Catalyst -> Phone -> PC

The Phone have a single VLAN und the PC should be in the nativ VLAN.

This is my config of one Port:

interface FastEthernet0/2
 switchport trunk encapsulation dot1q
 switchport trunk native vlan 2
 switchport mode trunk
 switchport voice vlan 70
 spanning-tree portfast


And is there a way to use one Port for nativ and untagged VLAN 70 simultaneously?

[Shashank Singh]

Hi Gerit,

The minimum requirement for QoS to work is that you enable QoS on the switch globally and trust the marking of the packet on the ingress interface. With QoS disabled, the priority marking on the packet will be ignored by the switch.

Phones send tagged traffic by default. Instead of having a trunk, it is advisable to have the following configuration:

interface FastEthernet0/2

switchport access vlan 2   ----> for PC (untagged)

switchport mode access

switchport voice vlan 70    ------>for phone (tagged)

It is not possible to have a switchport send untagged traffic on two vlans.

Hope this helps,

Shashank

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[kooper390]

Hi Shashank,

where can I switch globallythe QoS?

regards

[Shashank Singh · Accepted solution]

Hi Gerit,

On 3500XL platform QoS in enabled and all the ports are trusted by default unlike higher platform switches. In this case whatever marking the traffic comes with is used by the switch to prioritze the packet.

To mark the untagged packets on 3500XL switches, use switchport priority default <0-7> command.  You can override the CoS value set by the PC attached to the Cisco IP phone and use the configured port priority instead. This feature is called port-based re-classification. The switchport priority extend cos <0-7> interface command is issued to achieve this.

Details are available at http://www.cisco.com/en/US/products/hw/switches/ps607/products_qanda_item09186a0080116ffe.shtml

Cheers,

Shashank

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