Extreme Networks 200 Series Installation And User Manual page 164

Quality of Service (QoS)
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. The Summit 200 series switch has the capability of observing and
manipulating packet marking information with no performance penalty.
The documented capabilities for 802.1p priority markings or DiffServ capabilities 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.
NOTE
Re-marking DiffServ code points is supported through access lists. See Chapter 9, "Access Policies", for
more information.
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 29.
Figure 29: Ethernet Packet Encapsulation
802.1Q 802.1p 802.1Q
type priority VLAN ID
8100
Destination Source
IP packet CRC
address address
EW_024
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. The Summit 200 series switch
supports four hardware queues. The transmitting hardware queue determines the bandwidth
management and 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 41.
162 Summit 200 Series Switch Installation and User Guide