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350-401 Practice Question: In a Cisco QoS policy, what is the difference…
In a Cisco QoS policy, what is the difference between 'bandwidth' and 'bandwidth remaining' commands?
⚠ Common exam trap
Cisco often tests the misconception that 'bandwidth remaining' is an alternative way to allocate from total bandwidth, when in fact it specifically operates on the post-priority queue leftover bandwidth, making it essential for proper LLQ design.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
'bandwidth' allocates from the total bandwidth, while 'bandwidth remaining' allocates from the bandwidth left after priority queues.
The 'bandwidth' command allocates a guaranteed minimum bandwidth from the total interface bandwidth during congestion, while 'bandwidth remaining' allocates bandwidth only from the leftover bandwidth after the priority queue (LLQ) has taken its share. This distinction is critical in Cisco QoS policies where priority queues can consume a large portion of the link, and remaining bandwidth must be distributed among other classes using a ratio or percentage.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
There is no difference; both commands allocate bandwidth based on the total interface bandwidth.
Why it's wrong here
The two commands draw from fundamentally different, non-overlapping pools. The 'bandwidth' command reserves a fixed amount of the total interface bandwidth (or a policy-map's declared interface bandwidth) for a class, whereas 'bandwidth remaining' calculates a percentage based only on the residual bandwidth that exists after the priority queue and all explicitly allocated 'bandwidth' amounts have been removed. Thus, a class using 'bandwidth remaining' is not competing for the same pool as one using 'bandwidth', so treating them as identical is technically false.
- ✓
'bandwidth' allocates from the total bandwidth, while 'bandwidth remaining' allocates from the bandwidth left after priority queues.
Why this is correct
This is the correct answer. The 'bandwidth' command, in a CBWFQ policy map, explicitly allocates a guaranteed rate from the total interface bandwidth, and that rate is reserved under congestion. In contrast, 'bandwidth remaining' specifies a percentage or proportion of the bandwidth that is left after the priority queue (for low-latency traffic) and after all explicit 'bandwidth' allocations have been satisfied. Therefore, 'bandwidth remaining' is a fair-sharing mechanism for the leftover, non-priority bandwidth rather than a reservation from the full link capacity.
- ✗
'bandwidth' is used for output policies, while 'bandwidth remaining' is used for input policies.
Why it's wrong here
Both 'bandwidth' and 'bandwidth remaining' are used in output policies, not input policies. In MQC, these commands are configured in class maps within a policy map that is attached in the output direction, where CBWFQ and LLQ scheduling decisions apply. Input policies rely on policing mechanisms like the 'police' command to limit or mark packets; 'bandwidth' and 'bandwidth remaining' are scheduling/reservation tools that only have meaning in the egress direction where queueing occurs.
- ✗
'bandwidth' guarantees a minimum rate, while 'bandwidth remaining' sets a maximum rate.
Why it's wrong here
This option is incorrect because while 'bandwidth' does guarantee a minimum rate, claiming that 'bandwidth remaining' sets a maximum rate is false. 'bandwidth remaining' is a proportional guarantee, not a cap: it guarantees a class a specific share of the leftover bandwidth after priority queues are serviced, meaning the class can use as much as that share allows under congestion, but it does not impose a hard maximum like a policer's 'police' rate. Thus, 'bandwidth remaining' also provides a minimum bandwidth commitment, just from the residual pool rather than the total link.
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