Configuration Guide User guide

1964 FastIron Configuration Guide
53-1002494-02
QoS overview
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 1992.
• 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” on page 1740.
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 Figure 220 through
Figure 222.
Determining the trust level of a packet
Packet trust level is determined differently on FastIron X Series devices than on FastIron WS and
Brocade FCX and ICX series devices.
Figure 220 illustrates how FastIron X Series devices determine the trust level of a packet.
NOTE
Figure 220 is not applicable to the 48-port 10/100/1000 Mbps Ethernet POE interface module
(SX-FI48GPP). To determine the trust level of a packet for the SX-FI48GPP interface module, refer to
Figure 221.
As shown in the flowchart, the first criteria considered is whether the packet matches on an ACL
that defines a priority. Next, it checks if trust DSCP is enabled on the port. If this is not the case, the
packet is next classified based on the static MAC address. If this is not true and the packet is
tagged, the packet is classified with the 802.1p CoS value. If none of these is true, the packet is
next classified based on the ingress port default priority or the default priority of zero (0).