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802.1Q - Questions

* Is 802.1Q standard a tagging method or a protocol? Please explain the difference for each concept.

* 802.1Q tagging includes 3 priority bits for 802.1p standard. What IOS command is used to set up these bits? Are these bits only informative or have some QoS mechanism associated in both ports of the trunk? Please comment

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Re: 802.1Q - Questions

It can be called as a tagging method, as well as a Protocol standard from IEEE.

You can use policy maps to set COS bits. Check this link,

http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/fqos_c/fqcprt1/qcfcbmrk.htm#1005766

3 bits makes 8 different combinations, which means, 8 different QOS classes are defined. You can prioritize certain traffic (say voice) over other (say data), using COS bits at OSI layer 2 level. (just like TOS bits at OSI layer 3 level).

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Re: 802.1Q - Questions

* The COS bits at OSI layer 2 level are the same 3 bits that 802.1Q tagging includes over a trunk?

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