Traffic Policing and Shaping Configuring QoS
page 25-26 OmniSwitch AOS Release 7 Network Configuration Guide June 2013
Setting the DEI Bit
The Drop Eligible Indicator (DEI) bit setting is applied to packets marked yellow (non-conforming) as the
result of Tri-Color Marking (TCM) rate limiting. The TCM policier meters traffic based on user-config-
ured packet rates and burst sizes and then marks the metered packets as green, yellow, or red based on the
metering results. See “Configuring Tri-Color Marking” on page 25-24 for more information.
Yellow packets are assigned a high drop precedence, which means they are dropped first when the egress
port queues become congested. If there is no congestion on the queues, however, yellow packets are
retained and forwarded along to the next switch. When this occurs, the receiving switch does not know
that the packet was marked yellow by the transmitting switch.
Setting the DEI bit for yellow egress packets ensures that the upstream switch is made aware that the
packet was marked yellow. The upstream switch can then decide to drop the DEI marked packets first
when the network is congested. When a switch receives a yellow packet with the DEI bit set and DEI
mapping is enabled, the packet is mapped to an internal drop precedence or yellow color marking for the
switch.
The switch can be set globally so that DEI bit marking and mapping is enabled for all ports. Individual
ports can be configured to override the global setting
Configuring the DEI Bit Setting
By default, DEI bit marking (egress) and mapping (ingress) is disabled on all switch ports. The DEI bit
setting operation can be configured globally on the switch, or on a per-port basis.
To configure the global DEI bit setting operation to mark traffic egressing on QoS destination ports, use
the qos dei command with the egress parameter option. For example:
-> qos dei egress
To configure the switch to map ingress traffic marked with the DEI bit, use the qos dei command with the
ingress parameter option. For example:
-> qos dei ingress
To configure the DEI bit operation for an individual port, use the qos port dei with the ingress or egress
parameter option. For example:
-> qos port 1/10 dei egress
-> qos port 1/11 dei ingress
See the OmniSwitch CLI Reference Guide for more information about these commands.
Configuring Policy Bandwidth Policing
The policy action maximum bandwidth and policy action maximum depth commands are used to
configure QoS policy actions. Both actions are typically used in combination; the bucket size (depth)
determines how much over the maximum bandwidth the traffic can burst.
The maximum bandwidth and maximum depth actions are configured as part of a QoS policy in which the
condition specifies the type of traffic to rate limit. Maximum bandwidth policies are applied to source
(ingress) ports and/or flows. See the “Bandwidth Policing Example” on page 25-75.
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