Juniper JN0-650 Exam - Topic 4 Question 18 Discussion

The exhibit shows the Class of Service (CoS) transmit queue information for interface ge-0/0/11. To determine the correct behavior, we must analyze the bandwidth allocations and the queue limit settings:

Bandwidth Calculation (Option A): In Junos OS, when multiple queues are assigned specific percentages of bandwidth, the 'remainder' (represented by 'r') is the total interface bandwidth minus the sum of the explicitly configured percentages.

Bandwidth assigned to Queue 1 (EF) = 10%.

Bandwidth assigned to Queue 2 (AF) = 10%.

Bandwidth assigned to Queue 3 (NC) = 4%.

Total explicitly assigned = $10% + 10% + 4% = 24%$.

Remainder for Queue 0 (Best Effort) = $100% - 24% = 76%$.

'Limit: exact' Behavior (Option B): The exhibit shows that Queue 2 (assured-forwarding) has a Limit set to exact.

By default, a queue in Junos can consume more than its allocated bandwidth if other queues are idle.

However, when the exact keyword is applied to the transmit-rate (transmission rate), the queue is strictly rate-limited to its configured percentage.

This means that traffic in Queue 2 will be capped at 10% of the interface bandwidth regardless of whether the network is congested or not. If the traffic exceeds 10%, the excess will be dropped or buffered to match the exact rate.

Option C is incorrect because 100% of the bandwidth is not reserved for a single queue; it is distributed across four queues.

Option D is less accurate than B because it implies the drop behavior only occurs during congestion. The exact parameter enforces the limit even when the rest of the interface is completely idle.