Brocade Communications Systems Brocate Ethernet Access Switch 6910 - Manual (Page 845)

Brocade 6910 Ethernet Access Switch Configuration Guide 795
53-1002581-01
Layer 3/4 Priority Settings
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FIGURE 142 Showing CoS Values to Egress Queue Mapping
Layer 3/4 Priority Settings
Mapping Layer 3/4 Priorities to CoS Values
The switch supports several common methods of prioritizing layer 3/4 traffic to meet application
requirements. Traffic priorities can be specified in the IP header of a frame, using the priority bits in
the Type of Service (ToS) octet, or the number of the TCP/UDP port. If priority bits are used, the ToS
octet may contain three bits for IP Precedence or six bits for Differentiated Services Code Point
(DSCP) service. When these services are enabled, the priorities are mapped to a Class of Service
value by the switch, and the traffic then sent to the corresponding output queue.
Because different priority information may be contained in the traffic, this switch maps priority
values to the output queues in the following manner – The precedence for priority mapping is DSCP
Priority and then Default Port Priority.
NOTE
The default settings used for mapping priority values from ingress traffic to internal DSCP values are
used to determine the hardware queues used for egress traffic, not to replace the priority values.
These defaults are designed to optimize priority services for the majority of network applications. It
should not be necessary to modify any of the default settings, unless a queuing problem occurs with
a particular application.
Setting Priority Processing to DSCP or CoS
The switch allows a choice between using DSCP or CoS priority processing methods. Use the
Priority > Trust Mode page to select the required processing method.
CLI References
• “qos map trust-mode” on page 427
Command Usage
• If the QoS mapping mode is set to DSCP, and the ingress packet type is IPv4, then priority
processing will be based on the DSCP value in the ingress packet.