Access layer QoS

A little bit of frustration here..

I’ve got my CCNP ONT exam in two days which is a result of attending the Official Cisco Curriculum course and also using CBT Nuggets Training videos. Since studying the ONT course I’ve been spending most of time trying to translate my skills into the xDSL access world as that’s where I’ve got the routers – home and at work –  under my control to apply my new found queueing and congestion management skills. Since it actually isn’t fruitfull for me to spend too much time buggering about with xDSL routers as that’s slightly off curriculum and I need to keep focused, I was checking out my 3560 access switches which are part of the curriculum, which were configured back in the day by our all knowing wanky PBX maintenance company – Azzuri, which were at that time guised as MiTech.

They used the interface-range command and configured all the Fast Ethernet interfaces with the mls qos trust cos to take advantage of Voice VLANs as you can see here:-

interface FastEthernet0/12
switchport trunk encapsulation dot1q
switchport mode trunk
switchport voice vlan 10
no ip address
mls qos trust cos
no mdix auto
spanning-tree portfast

but if you pop into privileged mode and do a sh mls qos interface fas 0/12

3560SW#sh mls qos interface fas 0/12
FastEthernet0/12
QoS is disabled. When QoS is enabled, following settings will be applied
QoS is disabled. pass-through mode
When QoS is enabled, following settings will be applied
trust admin state: trust cos
trust mode: trust cos
trust enabled flag: ena
COS override: dis
default COS: 0
DSCP Mutation Map: Default DSCP Mutation Map
trust device: none

which fairly strongly states that QoS is DISABLED! Thanks, you bunch of Jockey’s from Azzuri.

So as a pre-requisite to enabling the mls qos trust command on the interface, you have to enable mls qos in Global configuration mode

3560SW(config)#mls qos

Then when you do a sh mls qos interface fas 0/12 you magically receive the answers you were expecting to see:-

3560SW#sh mls qos interface fas 0/12
FastEthernet0/12
trust admin state: trust cos
trust mode: trust cos
trust enabled flag: ena
COS override: dis
default COS: 0
DSCP Mutation Map: Default DSCP Mutation Map
trust device: none

Job done. Here’s hoping that’s a question in the ONT Exam on Thursday!

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