Configuration on a C6509 running CatOS: (prioritizing voice packets)
set port qos 1/1 vlan-based (part of vlan2)
set port qos 1/2 trust trust-cos (part of vlan3)
set qos enable
set qos cos-dscp-map 0 8 16 26 34 46 48 56
clear qos acl all
set qos acl ip VOICE dscp 46 ip any any
commit qos acl all
set qos acl map VOICE 2
In my opinion it is convenient that you can do both port based and vlan based QOS.
When a packet is part of a Vlan and a policy exists for that vlan, it will be applied.
When a packet arrives that's part of a vlan but no policy can be found for that vlan, the
policy of the port will be used.
So in this example when a packet comes in tagged as part of vlan 2, the ACL "VOICE" will
set the DSCP to 46. When a packet arrives on vlan 3 and no policy exists for this vlan,
the port policy will be used. The DSCP will be set mapped from the CoS value it had
because the CoS is trusted.
But from tests in my lab, it does not work like that. When set port qos trust trust-cos
is used, it will be the prefered way of handling IP packets all the time. The vlan based
policy will not be used. So you have to use vlans and apply policies for all vlans (if
not dscp = 0) or you specify the policies on all ports. But documentation states vlan
based supersedes port based config.
Is this correct or is my train of thought not in line with Cisco documentation?
The same configuration, but both part of the same vlan:
set port qos 1/1 vlan-based
set port qos 1/1 trust trust-cos
Can those commands exist together? Which policy will be used? vlan based or port based?