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QOS - CoS marking

I see marking defined as setting the frame 'CoS' value. For non ISL/802.1Q(non-native) there is no 'CoS' field but the docs state that the frame is marked with the port CoS. What is the meaning of 'marking' in these instances?

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Hall of Fame Super Blue

Re: QOS - CoS marking

Hi

As far as i know this is an internal COS marking that is not written into the actual packet, it is written into a separate packet called the Data bus header.

If the port is trusted and it is receiving 802.1q or ISL frames then it extracts the COS value and writes this into the Data bus header. If it is untrusted it will write the port COS value into the Data bus header.

See attached link for more details

http://www.cisco.com/en/US/products/hw/switches/ps700/products_tech_note09186a008014f8a8.shtml#topic2

HTH

Jon

3 REPLIES
Hall of Fame Super Blue

Re: QOS - CoS marking

Hi

Could you give a link to the docs you are referring to. You are correct in what you say, the 802.1p COS values are contained within the ISL or 802.1q tags.

Jon

New Member

Re: QOS - CoS marking

Hall of Fame Super Blue

Re: QOS - CoS marking

Hi

As far as i know this is an internal COS marking that is not written into the actual packet, it is written into a separate packet called the Data bus header.

If the port is trusted and it is receiving 802.1q or ISL frames then it extracts the COS value and writes this into the Data bus header. If it is untrusted it will write the port COS value into the Data bus header.

See attached link for more details

http://www.cisco.com/en/US/products/hw/switches/ps700/products_tech_note09186a008014f8a8.shtml#topic2

HTH

Jon

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