Extreme Networks ExtremeWare 7.2e Installation And User Manual page 116

Quality of Service (QoS)
on an application-specific basis. Extreme switch products have the capability of observing and
manipulating 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 or overwritten
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 18.
Figure 18: Ethernet packet encapsulation
802.1Q
type
8100
Destination Source
address address
Observing 802.1p Information
When ingress traffic that contains 802.1p prioritization information is detected by the switch, the traffic
is mapped to various hardware queues on the egress port of the switch. Eight hardware queues are
supported. The transmitting hardware queue determines the priority characteristics used when
transmitting packets.
To control the mapping of 802.1p prioritization values to hardware queues, 802.1p prioritization values
can be mapped to a QoS profile. The default mapping of each 802.1p priority value to QoS profile is
shown in Table 24.
Table 24: 802.1p Priority Value-to-QoS Profile Default Mapping
Priority Value QoS Profile
0 Qp1
1 Qp2
2 Qp3
3 Qp4
4 Qp5
5 Qp6
116
802.1p
priority
IP packet
802.1Q
VLAN ID
CRC
EW_024
ExtremeWare 7.2e Installation and User Guide