The provision of standards based configurations on Cisco based hardware deployed across an infrastructure aide in maintaining a deterministic known environment. This post attempts to identify what standard configuration I would apply to provide simple connectivity on a LAN for a single client with a VoIP enabled phone. In this example the client may actually be connected to the back of the phone.
# interface FastEthernet0/1
# description Client Data & VoIP
# switchport access vlan 100
# switchport auto qos voip trust
# switchport mls qos trust dscp
# switchport mode access
# switchport nonegotiate
# no ip address
# spanning-tree portfast
# spanning-tree bpduguard enable
The key thing in using auto qos is the overall understanding. If a packet is marked with class of service then unless a number of variables are applied the configuration will not be trusted further upstream. However, if you mark with DSCP (TOS not COS) then the Layer3 device should honour the markings. Please note that above we have used “auto qos” and then applied “mls qos trust dscp” in that order. If by chance you apply it the other way round then the “auto qos command will write by default an “mls qos trust cos” variable.