qos trust cos on 1638P

[coneil]

I am trying to determine if I need to add "qos trust cos" on all switch ports.

Devices will be passing DSCP values and I am mapping DSCP-COS

qos dscp-cos 0 8 16 24 32 40 46 48 to 0 1 2 3 4 5 7 6

interface gigabit-switchport 0/1

  description --->VOIP-VLAN10/PC<---

  spanning-tree edgeport

  no shutdown

  switchport voice vlan 10

  switchport voice-signaling vlan 10 cos 3 dscp 41

I noticed the statement below in the config

! DSCP to CoS mapping only operates on ports that have 'qos trust cos' applied

Also, when mapping DSCP-COS, will the switch pass original DSCP and mapped COS values on egress (to another switch) or only pass either DSCP or COS?

Thank you,

[Anonymous · Accepted solution]

:

Thank you for asking this question in the support community.  The command qos trust cos is disabled by default in the NV1638 on all ports.  Therefore, you will need to issue the command qos trust cos on every port where you desire the interface to trust cos if received 802.1P CoS values are considered valid (i.e., no need to reclassify) and do not need to be tagged with the default value. When set to untrusted, the default-cos value for the interface is used.

When mapping DSCP-COS, the switch will pass the original DSCP and mapped COS values on egress (to another switch).  I hope that makes sense, but please do not hesitate to reply to this post with additional information or questions.  I will be happy to help in any way I can.

Levi

[coneil]

Thank you.

That was clear, to confirm.

qos trust cos is not needed as DSCP will be mapped to COS and not be original COS from devices which would require qos trust cos

That leaves a question of should it be added for traffic on the (ingress)

Ingress traffic will pass original DSCP and mapped COS.

If qos trust cos is not added

Original DSCP will be mapped using DSCP-COS map

If qos trust cos is added

Mapped COS will be recognized

Both are the same QOS value, not sure if adding qos trust cos would be a benefit and decrease Adtran switch cpu by not requiring DSCP-COS map for ingress traffic.

Thank you,

Chris

[Anonymous]

Chris:

It depends on the network, and how much knowledge/control there is over the network.  If the overall goal is the monitor DSCP traffic and change the Layer 2 CoS value, then the DSCP-COS map may be what you need.  If you simply want to change the value of all CoS frames that arrive, then you can use the CoS queue.  If the CoS values are already set as desired when arriving into the switch, then trust seems appropriate.  These different functions serve various applications.  Here is the Configuring Ethernet Switch QoS and CoS in AOS guide, which explains in detail the different CoS and QoS setting for AOS switches.  Please, let me know what questions you have.

Levi

[Anonymous]

:

I went ahead and flagged the "Correct Answer" on this post to make it more visible and help other members of the community find solutions more easily. If you don't feel like the answer I marked was correct, feel free to come back to this post and unmark it and select another in its place with the applicable buttons.  If you still need assistance, we would be more than happy to continue working with you on this - just let us know in a reply.

Thanks,

Levi