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Voice QoS/CoS in Ethernet

tsaxelin
Level 1
Level 1

‎01-02-2001 01:57 AM - edited ‎03-12-2019 10:57 AM

The CIPT course material says that Cisco IP phones use the 802.1p field in the 802.1Q tag to classify voice packets with a CoS value of 5. What happens to the 802.1p field if we have ISL trunks between switches? Or do we have to run 802.1Q trunks in order to preserve the CoS bits?

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acgarcia
Level 4
Level 4

‎01-02-2001 08:40 PM

You are correct. You will need to run .q trunks to preserve the COS. I have heard of some people using the other mechnisms to repaint the packet when crossing ISL trunks (like using the PFC in a 6000)

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