User guide

9-12 E
XTREME
W
ARE
S
OFTWARE
U
SER
G
UIDE
Q
UALITY OF
S
ERVICE
(Q
O
S)
V
ERIFYING
MAC-B
ASED
Q
O
S S
ETTINGS
To verify any of the MAC-based QoS settings, use either the command
show fdb perm
or the command
show qosprofile <qosprofile>
E
XPLICIT
C
LASS OF
S
ERVICE
(802.1
P AND
D
IFF
S
ERV
) T
RAFFIC
G
ROUPINGS
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 may 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 and manipulating packet marking
information with no performance penalty.
Extreme products that use “i” chipset support DiffServ capabilities. Products that do not
use the “i” chipset s do not support DiffServ capabilities. 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
may be preserved across a routed switch boundary and DiffServ code points may be
observed or overwritten across a layer 2 switch boundary.
C
ONFIGURING 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 9-1.