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DSCP and L2 switch

By summers ·
Hi all,

Some L2 switch can trust DSCP on interfaces.
Why L2 switch can look at DSCP value in IP header? Is this just the way it works when you put the dscp trust command?

Any input will be appreciated.

Thanks in advance.

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by mshavrov In reply to DSCP and L2 switch

"Smart" Layer 2 switches are aware of what's going on on the Layer 3. First they check CoS (Layer 2 QoS marking), but then, if they "trust DSCP or IP Precedence", they analyze DSCP value, and convert them into the CoS using pre-defined map. Basically, DSCP is used on the Layer 3 to do Access Lists and queueing based on the priority, but most of "trust" happens on the Layer 2.

Good luck,

CCNP, CCDP, CCSP, Cisco Voice, CCIE Voice Written, etc.

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by summers In reply to DSCP and L2 switch

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