A Fair Information Rate (FIR) can be configured on a queue to use two additional scheduling priorities (expedited queue within FIR and best-effort queue within FIR). The queues which operate below their FIR are always served before the queues operating at or above their FIR. See Queue scheduling for more information about queue scheduling.
The FIR does not affect the queue packet profiling operation which is dependent only on the queue's CIR rate at the time that the packet is scheduled; the FIR is purely a scheduling mechanism.
When defining the FIR for a queue, the value specified is the administrative FIR for the queue. The router has a number of native rates in hardware that it uses to determine the operational FIR for the queue. The user has some control over how the administrative FIR is converted to an operational FIR if the hardware does not support the exact FIR specified. See Adaptation rule for more information about the interpretation of the administrative FIR.
The FIR rate is supported in SAP ingress QoS policies (for ingress SAP and subscriber queues), ingress queue group templates (for access ingress queue group queues), and network queue policies (for ingress and egress network queues). The FIR can also be configured on system-created ingress shared queues. The FIR is configured in kb/s in a SAP ingress QoS policy and an ingress queue group template, and as a percent in a SAP ingress QoS policy, network queue policy, and ingress shared queue. The default FIR rate is zero (0) with an adaptation rule closest.
FIR is only supported on FP4-based hardware and is ignored when the related policy is applied to FP2- or FP3-based hardware.
The FIR rate is not used within virtual hierarchical scheduling (see Virtual hierarchical scheduling), but it is capped by the resulting operational PIR.
A FIR should not be configured in a SAP ingress QoS policy, ingress queue group template, or network queue policy associated with a LAG which spans FP4-based and FP2- or FP3-based hardware as the resulting operation could be different depending on which hardware type the traffic uses.