Extreme Networks ExtremeWare XOS 10.1, Manual

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86 ExtremeWare XOS 10.1 Concepts Guide
Quality of Service (QoS)
Explicit Class of Service (802.1p and DiffServ) Traffic Groupings
This category of traffic groupings describes what is sometimes referred to as explicit packet marking, and
refers to information contained within a packet intended to explicitly determine a class of service. That
information includes:
• IP DiffServ code points, formerly known as IP TOS bits
• Prioritization bits used in IEEE 802.1p packets
An advantage of explicit packet marking is that the class of service information can be carried
throughout the network infrastructure, without repeating what can be complex traffic grouping policies
at each switch location. Another advantage is that end stations can perform their own packet marking
on an application-specific basis. Extreme switch products have the capability of observing packet
marking information with no performance penalty.
The documented capabilities for 802.1p priority markings or DiffServ capabilities (if supported) are not
impacted by the switching or routing configuration of the switch. For example, 802.1p information can
be preserved across a routed switch boundary and DiffServ code points can be observed across a layer 2
switch boundary.
Configuring 802.1p Priority
Extreme switches support the standard 802.1p priority bits that are part of a tagged Ethernet packet.
The 802.1p bits can be used to prioritize the packet, and assign it to a particular QoS profile.
When a packet arrives at the switch, the switch examines the 802.1p priority field maps it to a specific
hardware queue when subsequently transmitting the packet. The 802.1p priority field is located directly
following the 802.1Q type field, and preceding the 802.1Q VLAN ID, as shown in Figure 7.
Figure 7: Ethernet packet encapsulation
• DiffServ (IP TOS)
• 802.1P
Physical Groupings
• Source port
Table 13: Traffic Groupings by Precedence (continued)
EW_024
Source
address
802.1Q
type
802.1p
priority
802.1Q
VLAN ID
IP packet CRC
Destination
address
8100