Brocade Multi-Service IronWare QoS and Traffic Management Configuration Guide (Supporting R05.6.00) - Manual (Page 17)

Multi-Service IronWare QoS and Traffic Management Configuration Guide 3
53-1003037-02
Traffic policing on Brocade NetIron CES and Brocade NetIron CER devices
1
The CIR bucket
The CIR rate limiting bucket is defined by two 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 the line rate (bandwidth) for an interface
expressed in bits per second (bps) and cannot be larger than the line rate of the port. CIR-defined
traffic that does not use the available CIR rate accumulates credits that be used 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 is higher than the CIR rate to traffic that
exceeds the CIR rate. The bandwidth in the CBS rate accumulates during periods when traffic that
has been defined by a policy does not use the full CIR rate available. 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 the 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, two parameters define 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.
• For policy-map based rate-limiting, the committed burst in a traffic policing policy cannot be
less than 1250 bytes and cannot be more than the port’s line rate in bytes.
• For non policy-map based rate-limiting, the maximum burst in a traffic policing policy cannot be
less than 10000 bits and cannot be more than the port’s line rate in bits.
• Control packets are not subject to traffic policing.
• Source MAC address with Virtual Leased Line (VLL) endpoints are not subject to traffic policing.
• Up to four different sets of excess parameters are supported. Delete or unbind other policy
maps from other interfaces. You can also change the excess parameters in the policy map to
match one of the existing profiles to share the Remark Profile Tables.
• BUM rate-limit may not work properly with a lower configured-rate and bursty traffic.