JN0-106 Networking Fundamentals Practice Question
A network engineer sees an unknown unicast flood on a Juniper EX switch. Which mechanism is most effective at reducing such floods?
⚠ Common exam trap
Test-takers frequently confuse storm control (which rate-limits flooded traffic) with broadcast suppression or MAC learning controls, and may incorrectly think that increasing aging time or disabling MAC learning will reduce flooding, when in fact those actions either have no effect or worsen the problem.
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
✓
Enable storm control for unknown unicast traffic.
Unknown unicast flooding occurs when a switch does not have a MAC address entry for a destination, causing it to flood the frame out of all ports in the VLAN except the ingress port. Storm control for unknown unicast traffic (set using `set ethernet-switching-options storm-control interface <interface> unknown-unicast`) directly limits the rate of such flooded traffic, preventing excessive bandwidth consumption. This is the most effective mechanism because it specifically targets and rate-limits unknown unicast floods without altering MAC learning or aging behavior.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Enable storm control for unknown unicast traffic.
Why this is correct
Storm control on Junos allows you to define a threshold for unknown unicast traffic, either as a percentage of interface bandwidth or as packets per second. When the unknown unicast flood exceeds that threshold, the switch drops excess traffic or shuts down the affected interface until it recovers, preventing the flood from saturating the network. This is a practical, policy-based mitigation because it does not require knowing every endpoint and can be applied per interface and per VLAN.
- ✗
Configure static MAC addresses for all endpoints.
Why it's wrong here
Configuring static MAC addresses would require manually binding every endpoint MAC to its specific port and VLAN in the forwarding table. While this would eliminate flooding for those exact addresses, it is operationally unscalable in any real enterprise network and breaks whenever endpoints are added, replaced, or migrate. Any unconfigured address will still trigger unknown unicast flooding, so this approach only masks the symptom for a small static subset.
- ✗
Increase the MAC address table aging time.
Why it's wrong here
Raising the MAC-table aging time keeps dynamically learned entries in the forwarding table for longer, so an address that was recently active is less likely to have aged out when a frame arrives. However, it cannot help with destinations that have never been seen or with hosts that have been idle longer than the increased timer, both of which will still produce an unknown unicast flood. Aging-time tweaks delay the onset of flooding for active endpoints but do not cap the rate or breadth of flood traffic.
- ✗
Disable MAC learning on trunk interfaces.
Why it's wrong here
MAC learning is what records source addresses and their ingress ports in the MAC table, enabling precise frame forwarding. Disabling MAC learning on a trunk means the switch no longer learns endpoints behind that trunk, so frames to those destinations are treated as unknown and are flooded out all ports, including the trunk itself. This increases the unknown unicast flood volume and degrades the entire VLAN instead of protecting it.
Visual reference
Quick reference
Access Control Model Comparison
| Model | Acronym | Who Controls Access? | Best For |
|---|---|---|---|
| Discretionary Access Control | DAC | Resource owner | Small teams, file shares |
| Mandatory Access Control | MAC | System / security labels | Classified govt / military |
| Role-Based Access Control | RBAC | Administrator (via roles) | Enterprise environments |
| Attribute-Based Access Control | ABAC | Policy engine (user + resource attributes) | Fine-grained, dynamic policies |
| Rule-Based Access Control | RuBAC | System rules / ACLs | Firewall rules, network ACLs |
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This JN0-106 practice question is part of Courseiva's free Juniper Networks certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the JN0-106 exam.