Classification; How Traffic Is Classified And Marked - Alcatel-Lucent OmniSwitch AOS Release 7 Manual

Classification

Classification is the process of identifying certain types of network traffic (flows) and then, if necessary,
marking a specific flow or group of flows with a priority (class of service) value. The class of service
(CoS) value assigned is then used by other QoS features to determine how the flow is treated throughout
the network.
The CoS value assigned to a specific flow is based on one of the following technologies:
•
IP Precedence—Type of Service (ToS) or Differentiated Services (DiffServ).
ToS refers to using the three precedence bits of the ToS field in an IP packet to specify a priority value
ranging from 0 (lowest) to 7 (highest).
DiffServ uses the DiffServ Code Point (DSCP) value specified in the first 6 bits of the ToS field. The
DSCP determines the CoS by specifying a per-hop behavior (PHB) for a specific flow or group of
flows. The PHB indicates the forwarding behavior of a flow by specifying bandwidth, queueing
schemes, and criteria for dropping packets.
•
Layer 2 802.1p Priority
The 802.1p priority value is specified in the Tag Control Info (TCI) field of an Ethernet frame. This
value also ranges from 0 (lowest) to 7 (highest) and maps to the ToS precedence values.
The OmniSwitch 10K virtual output queuing (VOQ) capability uses these CoS values to determine the
forwarding treatment by prioritizing flows based on application and network requirements. For more infor-
mation about VOQ and queue (congestion) management, see

How Traffic is Classified and Marked

The OmniSwitch 10K provides the following tools and techniques for classifying network traffic:
•
QoS Policy Rules
A policy (or a policy rule) is made up of a condition and an action. The condition specifies parameters
that the switch examines in incoming flows, such as destination address or Type of Service (ToS) bits.
The action specifies what the switch does with a flow that matches the condition; for example, it can
queue the flow with a higher priority, or reset the ToS bits. See
for more information.
•
Access Control Lists (ACLs)
ACLs are QoS policies used to control whether or not packets are allowed or denied at the switch or
router interface. ACLs are sometimes referred to as filtering lists and may also specify priority-setting
actions. See "Using Access Control Lists" on page 21-59
•
Port-based QoS
Individual ports are configured to either trust (recognize) or not trust (don't recognize) existing 802.1p
or ToS/DSCP values within a packet or to apply a user-defined default classification value. Port-based
QoS often works in conjunction with QoS policy rules to prioritize packet flows. By default, all switch
ports are untrusted. See
When packets ingress on a switch port, the packets are classified and marked as follows:
•
If a packet matches a QoS policy rule that sets a new priority value (802.1p or ToS/DSCP), the egress
priority for the packet is set using the value specified in the rule.
page 21-6
"Configuring Trusted Ports" on page 21-8
OmniSwitch AOS Release 7 Network Configuration Guide
"Congestion Management" on page
"QoS Policy Overview" on page 21-26
for more information.
for more information.
21-10.
March 2011