Which two statements are true about bandwidth guarantee? (Choose two.)

A.
When congestion is present, the priority command doesn’t allow exceeding the allocated rate

B.
When congestion isn’t present, the priority command doesn’t allow exceeding the allocated rate

C.
When congestion is present, the priority command allows exceeding the allocated rate

D.
When congestion isn’t present, the priority command allows exceeding the allocated rate

Explanation:
During congestion conditions, the traffic class is guaranteed bandwidth equal to the specified rate.
(Recall that bandwidth guarantees are only an issue when an interface is congested.) In other
words, the priority command provides a minimum bandwidth guarantee.
In addition, the priority command implements a maximum bandwidth guarantee. Internally, the
priority queue uses a token bucket that measures the offered load and ensures that the traffic
stream conforms to the configured rate. Only traffic that conforms to the token bucket is
guaranteed low latency. Any excess traffic is sent if the link is not congested or is dropped if the
link is congested.

“The purpose of the built-in policer is to ensure that the other queues are serviced by the queueing
scheduler. In the original Cisco priority queueing feature, which uses the priority-group and
priority-list commands, the scheduler always serviced the highest priority queue first. In extreme
cases, the lower priority queues rarely were serviced and effectively were starved of bandwidth.
The real benefit of the priority command—and its major difference from the bandwidth
command—is how it provides a strict de-queueing priority to provide a bound on latency. Here is
how the Cisco IOS Configuration Guide describes this benefit: “A strict priority queue (PQ) allows
delay-sensitive data such as voice to be de-queued and sent before packets in other queues are
de-queued…..”