Dell PowerConnect 8100 CLI Reference Guide - Page 637

- Untrusted Port Default Priority • Queue Configuration This enables PowerConnect switches to support a wide variety of delay sensitive video and audio multicast applications. CoS mapping tables, port default priority, and hardware queue parameters may be configured on LAG interfaces as well as physical port interfaces. Queue Mapping The priority of a packet arriving at an interface is used to steer the packet to the appropriate outbound CoS queue through a mapping table. Network packets arriving at an ingress port are directed to one of n queues in an egress port(s) based on the translation of packet priority to CoS queue. The CoS mapping tables define the queue used to handle each enumerated type of user priority designated in either the 802.1p, IP precedence, or IP DSCP contents of a packet. If none of these fields are trusted to contain a meaningful COS queue designation, the ingress port can be configured to use its default priority to specify the CoS queue. CoS queue mappings use the concept of trusted and untrusted ports. A trusted port is one that takes at face value a certain priority designation within arriving packets. Specifically, a port may be configured to trust one of the following packet fields: • 802.1p User Priority • IP Precedence • IP DSCP Packets arriving at the port ingress are inspected and their trusted field value is used to designate the COS queue that the packet is placed when forwarded to the appropriate egress port. A mapping table associates the trusted field value with the desired COS queue. Alternatively, a port may be configured as untrusted, whereby it does not trust any incoming packet priority designation and uses the port default priority value instead. All packets arriving at the ingress of an untrusted port are directed to a specific COS queue on the appropriate egress port(s) in accordance with the configured default priority of the ingress port. This QoS Commands 637