Trust CoS pass through DSCP

incoming CoS > cos-dscp map > internal dscp > dscp-cos map > egress queue

> egress cos incoming dscp -------------------------------------------------------------- > egress dscp

Example: QoS Mechanisms on the Catalyst 2950 Switch

The example in the illustration provides a block diagram of the QoS mechanisms on the Catalyst 2950 switch.

• QoS ACLs using Layer 2, 3, and 4 access control parameters

- Source/destination MAC address, 16-bit Ethertype, source/destination IP address, TCP/UDP source or destination port number

• QoS ACLs using Layer 2, 3, and 4 access control parameters

- Source/destination MAC address, 16-bit Ethertype, source/destination IP address, TCP/UDP source or destination port number

• QoS based on DSCP classification; Support for 13 widely used, well-known DSCP values (0, 8, 10, 16, 18, 24, 26, 32, 34, 40, 46, 48, and 56)

• CoS override per port

On incoming packets, classification and reclassification are performed by identifying packet groups using either DSCP or CoS. Policing and metering, if configured, are then performed on the packets to ensure compliance to configure rates. Marking is the last action performed on incoming packets, based on the CoS-to-DSCP or DSCP-to-CoS mappings.

Outgoing packets are scheduled and queued for congestion control. There are four queues per port and packets are scheduled based on WRR and strict priority scheduling.

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