Auto QOS Configuration

[Mokhalil82]

Hi

I have configured Auto QOS for the first time and just want to make sure I have done it right. I am using avaya phones (so enabled lldp) so my access switches have voice and data vlans on the access ports. The access switches are then trunked up to the core switch. 

On my access ports and my trunk uplink, I have configured the following auto qos commands:

auto qos trust

mls qos trust dscp

By default when using the "auto qos trust" command, it trusts cos. But I read somewhere that we can trust dscp on the access ports as the phones should be marking the voip traffic as dscp ef.

Does this sound correct or shall I trust cos on the access ports and dscp on the uplinks?

Thanks

[Mark Malone · Accepted solution]

Ok so cos is layer 2 header , dscp goes to layer 3 header but your phones can mark at cos 5 the mls will map the cos 5 to dscp 46 using this mls qos map cos-dscp 0 8 16 24 32 46 48 56 , the uplink will see the remapped 5 - 46 an pass it upstream at correct value

what you want to make sure is when the traffic leaves the switch in wireshark the EF value is 46 in the voice packet that's why the uplink must be trust dscp , from experience never had an issue setting it to either cos or dscp at access port once your cos-dscp mapping value is set correctly to match the chart the switch always pushes it out in WS as ef 46

make sure for voice cos 5 it maps to ef 46

see this chart for cos-dscp conversions

http://www.netcontractor.pl/blog/wp-content/uploads/2010/06/QoS-Values-Calculator-v21.jpg

[Mokhalil82]

Thanks Mark for clearing that up