Notes on Cos (Layer2) / DSCP (Layer3)


If VLANs are used, the access point can use the CoS settings within IEEE 802.1p, and the DSCP-to-CoS mapping is done by the upstream device.

An Example of a switch config :

mls qos map cos-dscp 0 8 16 24 34 46 48 56
! Modifies CoS-to-DSCP mapping to map CoS 5 to DSCP 46 (EF)
! and CoS 4 to DSCP 34 (AF41)

mls qos map policed-dscp 0 24 34 to 8
! Excess data & voice traffic will be remarked to Scavenger (CS1)

If the CoS settings of IEEE 802.1p are not used, the access point uses the DSCP settings.

If switch infrastructure does not mark frames or packets with IEEE 802.1p CoS or IP TOS or DSCP, then the VLAN default CoS on the access point is used to apply a specific wireless CoS.

The classification flowchart of a 3560 switch :

A nice link of Qos configuration on a 3560 :
http://www.cisco.com/en/US/docs/switches/lan/catalyst3560/software/release/12.2_20_se/configuration/guide/swqos.html

About Joost van der Made

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