Brocade FastIron Ethernet Switch Traffic Management Guide - Manual (Page 14)

Feature ICX 6430 ICX 6450 FCX ICX 6610 ICX 6650 FSX 800
FSX 1600 ICX 7750
User-configurable scheduler profiles 08.0.01 08.0.01 08.0.01 08.0.01 08.0.01 No
08.0.10
QoS overview
Quality of Service (QoS) features are used to prioritize the use of bandwidth in a switch. When QoS
features are enabled, traffic is classified as it arrives at the switch, and processed through on the basis
of configured priorities. Traffic can be dropped, prioritized for guaranteed delivery, or subject to limited
delivery options as configured by a number of different mechanisms.
This chapter describes how QoS is implemented and configured in FastIron devices.
Classification is the process of selecting packets on which to perform QoS, reading the QoS
information, and assigning a priority to the packets. The classification process assigns a priority to
packets as they enter the switch. These priorities can be determined on the basis of information
contained within the packet or assigned to the packet as it arrives at the switch. Once a packet or
traffic flow is classified, it is mapped to a forwarding priority queue.
Packets on Brocade devices are classified in up to eight traffic classes with values from 0 to 7.
Packets with higher priority classifications are given a precedence for forwarding.
Processing of classified traffic
The trust level in effect on an interface determines the type of QoS information the device uses for
performing QoS. The Brocade device establishes the trust level based on the configuration of various
features and whether the traffic is switched or routed. The trust level can be one of the following:
• Ingress port default priority.
• Static MAC address.
• Layer 2 Class of Service (CoS) value - This is the 802.1p priority value in the Ethernet frame. It
can be a value from 0 through 7. The 802.1p priority is also called the Class of Service .
• Layer 3 Differentiated Services Code Point (DSCP) - This is the value in the six most significant
bits of the IP packet header 8-bit DSCP field. It can be a value from 0 through 63. These values
are described in RFCs 2472 and 2475. The DSCP value is sometimes called the DiffServ value .
The device automatically maps the DSCP value of a packet to a hardware forwarding queue.
Refer to
Viewing QoS settings on page 41.
• ACL keyword - An ACL can also prioritize traffic and mark it before sending it along to the next
hop. This is described under "QoS options for IP ACLs" section in the FastIron Ethernet Switch
Security Configuration Guide .
Given the variety of different criteria, there are many 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 schemes illustrated in the Determining a packet
trust level - FSX devices through Determining a packet trust level - FCX, and ICX devices figures.
Determining the trust level of a packet
Packet trust level is determined differently on FSX devices than on FCX, and ICX series devices.
The following figure illustrates how FSX devices determine the trust level of a packet.
QoS overview
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