Foundry Configuration Guide for the FESX, FSX, and FWSX
13 - 2 © Foundry Networks, Inc. December 22, 2005
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 the FESX, FSX, and FWSX are classified in up to eight traffic classes with values between 0 and 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 Foundry device establishes the trust level based on the configuration of various features and if 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 – 7. The 802.1p priority is also called the Class of Service.
• Layer 3 Differentiated Service codepoint (DSCP) – This is the value in the six most significant bits of the IP
packet header’s 8-bit DSCP field. It can be a value from 0 – 63. These values are described in RFCs 2472
and 2475. The DSCP value is sometimes called the DiffServ value. The device automatically maps a
packet's DSCP value to a hardware forwarding queue. See “Viewing QoS Settings” on page 13-15".
• ACL keyword – An ACL can also prioritize traffic and mark it before sending it along to the next hop. This is
described in the ACL chapter in the section “QoS Options for IP ACLs” on page 12-23.
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 13.1
Determining a Packet’s Trust Level
Figure 13.1 illustrates how the Foundry device determines a packet’s trust level.
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