Processing of classified traffic – Brocade BigIron RX Series Configuration Guide User Manual

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BigIron RX Series Configuration Guide

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Classification

•

Packet priority – Depending on the Trust level set, a packet can be classified by either the
802.1p priority or DSCP value that it has when it arrives at the switch. If no trust level is set, the
packet will default to a priority set by earlier criteria. By default, the trust level is set to 802.1p.
In addition, you can configure a port to override the DSCP value for every packet that arrives on
it to a user-configured value.

Processing of classified traffic

Given the variety of different criteria, there are multiple possibilities for traffic classification within a
stream of network traffic. For this reason, the priority of packets must be resolved based on which
criteria takes precedence. Precedence follows the scheme illustrated in

Figure 87

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 96

through

Table 99

. The

mapping between the internal priority and the forwarding queue cannot be changed.

Table 96

through

Table 99

show the default QoS mappings on the device, which are used if the

trust level for CoS or DSCP is enabled.

802.1p Priority

Trust Level
Set to COS
(default)