Brocade Multi-Service IronWare QoS and Traffic Management Configuration Guide (Supporting R05.6.00) - Manual (Page 32)

18 Multi-Service IronWare QoS and Traffic Management Configuration Guide
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Traffic policing on the Brocade device
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The CIR bucket
The CIR rate limiting bucket is defined by two separate parameters: the CIR rate, and the
Committed Burst Size (CBS) rate. The CIR rate is the maximum number of bits a port is allowed to
receive or send during a one-second interval. The rate of the traffic that matches the traffic policing
policy can not exceed the CIR rate. The CIR rate represents a portion of an interface's line rate
(bandwidth), expressed in bits per second (bps) and it cannot be larger than the port’s line rate.
CIR-defined traffic that does not use the CIR rate available to it accumulates credits that it can use
later in circumstances where it temporarily exceeds the CIR rate.
When traffic exceeds the bandwidth that has been reserved for it by the CIR rate defined in its
policy, it becomes subject to the CBS rate. The CBS rate provides a rate higher than the CIR rate to
traffic that exceeded its CIR rate. The bandwidth in the CBS rate, as expressed in bytes, is
accumulated during periods of time when traffic that has been defined by a policy does not use the
full CIR rate available to it. Traffic is allowed to pass through the port for a short period of time at
the CBS rate.
When inbound or outbound traffic exceeds the bandwidth available for the defined CIR and CBS
rates, it is either dropped, or made subject to the conditions set in it EIR bucket.
The EIR bucket
The EIR bucket provides an option for traffic that has exceeded the conditions set by policy for the
CIR bucket. In the EIR bucket, there are two parameters that define the traffic that is available: the
Excess Information Rate (EIR) and the Excess Burst Size (EBS) rate. The EIR and EBS operate
exactly like the CIR and CBS except that they only act upon traffic that has been passed to the EIR
bucket because it could not be accommodated by the CIR bucket. Like the CIR, the EIR provides an
initial bandwidth allocation to accommodate inbound and outbound traffic. If the bandwidth
provided by the EIR is insufficient to accommodate the excess traffic, the defined EBS rate provides
for burst traffic. Like the CBS, the bandwidth available for burst traffic from the EBS is subject to
the amount of bandwidth that is accumulated during periods of time when traffic that has been
allocated by the EIR policy is not used.
In addition, to providing additional bandwidth for traffic that exceeds that available for the CIR
bucket, traffic rate limited by the EIR bucket can have its excess priority and excess dscp values
changed. Using this option, priority parameters are set following the EBS value that change the
priority of traffic that is being rate limited using the EIR bucket.
Configuration considerations
• Only one type of traffic policing policy can be applied on a physical port. For example, you
cannot apply port-and-ACL-based and port-based traffic policing policies on the same port.
• When a VLAN-based traffic policing policy is applied to a port, all the ports controlled by the
same packet processor are rate limited for that VLAN. You cannot apply a VLAN-based traffic
policing policy on another port of the same packet processor for the same VLAN ID.
• The Multi-Service IronWare software supports VLAN-based traffic policing that can limit tagged
and untagged packets that match the VLAN ID specified in the policy. Untagged packets are
not subject to traffic policing.
• The maximum burst in a traffic policing policy cannot be less than the average rate and cannot
be more than the port’s line rate.
• Control packets are not subject to traffic policing.
• Source MAC address with Virtual Leased Line (VLL) endpoints are not subject to traffic policing.