DSCP-to-CoS Mapping

[Anonymous]

- The default DSCP-to-CoS mapping for CoS 5 is DSCP 40

- My VoIP traffic is marked with DSCP EF (46), if I want DSCP EF mapped to COS 5, I will need to change the DSCP-to-CoS Mapping from 40 to 46 correct?

- The traffic that is tagged with a COS 5, will that traffic retain the COS 5 between Ethernet switches.

[Anonymous · Accepted solution]

Jeff:

Thank you for asking this question in the support community.  I will try to answer your questions as best as I can.  Also, please review this guide for additional information about Ethernet Switch QoS Configuration.

CoS values can be determined based on the packet’s DSCP value (if DSCP-to-CoS mapping is enabled using the qos dscp-cos command). If DSCP-to-CoS mapping is enabled, CoS values are altered when specified DSCP values are detected on inbound traffic.  On most of the switching platforms DSCP-to-CoS mapping is disabled by default.  However, when DSCP-to-CoS mapping is enabled, then by default the mapping is shown in the table below:

DSCP	0	8	16	24	32	40	48	56
CoS	0	1	2	3	4	5	6	7

If you want DSCP 46 to be mapped to a CoS of 5, then you will need the following commands:

(config)# qos dscp-cos

(config)# qos dscp-cos 46 to 5

When the CoS is tagged with a value of 5, that value will be retained throughout the switching network--as long as the other switches are configured to trust CoS values.

I hope that makes sense, but please do not hesitate to reply with any additional questions or information.  I will be happy to help in any way I can.

Levi

[Anonymous]

Jeff:

I went ahead and flagged this post as “Assumed Answered.”  If any of the responses on this thread assisted you, please mark them as either Correct or Helpful answers with the applicable buttons.  This will make them visible and help other members of the community find solutions more easily.  If you still need assistance, I would be more than happy to continue working with you on this - just let me know in a reply.

Levi

[Anonymous]

@jeff:

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