Dell PowerConnect B-RX - Page 554

478 BigIron RX Series Configuration Guide
53-1002253-01
Classification
18
FIGURE 87 Priority resolution
As shown in the figure, the first criteria considered are port-based, MAC-based, and port-based
VLAN classifications. The packet is primarily classified with the higher of these two criteria. Next,
the packet is classified based on the trust level set. If there is no trust level set, the packet retains
the port or MAC derived QoS classification, If a trust level is set, the packet will either take the
802.1p or DSCP priority depending on which is set as the trust level.
Once a packet is classified by one of the procedures mentioned, it is mapped to an internal
forwarding queue in the BigIron RX. There are four queues designated as 0 to 3. The internal
forwarding priority maps to one of these four queues as shown in Table 91 through Table 94. The
mapping between the internal priority and the forwarding queue cannot be changed.
Table 91 through Table 94 show the default QoS mappings on the device, which are used if the
trust level for CoS or DSCP is enabled.
TABLE 91 Default QoS mappings, columns 0 to 15
DSCP value 0123456789101112121415
802.1p (COS)
Value
0000000011111111
DSCP value 0123456789101112121415
Internal
Forwarding
Priority
0000000011111111
Forwarding
Queue
0000000000000000
802.1p Priority
Trust Level
Set to COS
(default)
Determine
Trust Level
Set Classification to
Higher of both Inputs
Port-based
Classification
MAC-based
Classification
Port-based VLAN
Classification
DSCP Priority
No
Trust Level
Set
Trust Level
Set to DSCP