Brocade FastIron Ethernet Switch Traffic Management Guide - Manual (Page 21)

level is DSCP. Refer to Changing the DSCP to internal forwarding priority mappings on page 34.
• VLAN priority (802.1p) to hardware forwarding queue - You can change the mapping between the
802.1p value and hardware forwarding queue from the default value. Refer to
Changing the VLAN
priority 802.1p to hardwareforwarding queue mappings on page 35.
QoS for Brocade stackable devices
Brocade FastIron units in a traditional stack support QoS. Units in a stack communicate the stack
topology information and other proprietary control information through the stacking links. For more
information about stacking links and traditional stack technology, refer to the FastIron Ethernet Switch
Stacking Configuration Guide .
In addition to control information, the stacking links also carry user network data packets. In a traditional
stack topology, the priority of stacking-specific control packets is elevated above that of data path
packets, preventing loss of control packets, and timed retries that affect performance. This prioritization
also prevents stack topology changes that may occur if enough stack topology information packets are
lost.
Traditional stack technology reserves one QoS profile to provide a higher priority for stack topology and
control traffic.
QoS profile restrictions in a traditional stack
In a stacking topology, because CoS level 7 is reserved for stacking, quality profiles for qosp7 cannot
be configured. If an attempt is made to configure a profile for qosp7, the system ignores the
configuration.
NOTE
This applies only when the device is operating in stacking mode. It does not apply to stand-alone
devices.
QoS behavior for trusting Layer 2 (802.1p) in a traditional stack
By default, Layer 2 trust is enabled. Because priority 7 is reserved for stacking control packets, any
ingress data traffic with priority 7 is mapped to internal hardware queue 6. All other priorities are
mapped to their corresponding queues.
QoS behavior for trusting Layer 3 (DSCP) in a traditional stack
When the trust dscp mode is enabled, packets arriving with DSCP values 56 to 63 are mapped to
internal hardware queue 6. All other DSCP values are mapped to their corresponding internal hardware
queues.
QoS behavior on port priority and VLAN priority in a traditional stack
Port priority has a higher precedence than the 802.1p priority examination. If port priority is set to 7, all
incoming traffic is mapped to internal hardware queue 6.
QoS for Brocade stackable devices
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