JN0-106 Networking Fundamentals Practice Question
Exhibit
MAC address table: VLAN MAC address Type Age Interfaces default 00:00:5e:00:01:01 Static - ge-0/0/0.0 vlan10 00:0c:29:2a:3b:4c Dynamic 20 ge-0/0/1.0 vlan10 00:0c:29:2a:3b:4d Dynamic 10 ge-0/0/2.0 vlan20 00:0c:29:2a:3b:4e Dynamic 5 ge-0/0/3.0
Refer to the exhibit. A frame with destination MAC 00:0c:29:2a:3b:4d arrives on interface ge-0/0/0. What action will the switch take?
⚠ Common exam trap
Candidates often assume a switch always floods unknown unicast frames, but the question explicitly provides a known destination MAC, so the correct action is unicast forwarding, not flooding.
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
✓
Forward the frame out of ge-0/0/2 only
The switch learns MAC addresses and their associated VLANs from incoming frames. Since the destination MAC 00:0c:29:2a:3b:4d is already in the MAC address table and mapped to interface ge-0/0/2 within the same VLAN, the switch forwards the frame only out of ge-0/0/2. This is the fundamental behavior of transparent bridging: unicast frames are forwarded only to the port where the destination MAC was last seen.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Flood the frame to all ports except ge-0/0/0
Why it's wrong here
The Ethernet switching table in Junos contains a learned MAC address entry for the destination, so the frame is a known unicast. Flooding is only performed for unknown unicast, broadcast, or multicast frames, where the destination is not in the table. Since the entry exists and points to ge-0/0/2, flooding to all ports except the ingress would be unnecessary and incorrect.
- ✓
Forward the frame out of ge-0/0/2 only
Why this is correct
This is the correct behavior because Junos performs a lookup of the destination MAC address in the Layer 2 forwarding table. The entry for 00:0c:29... lists ge-0/0/2 as the egress interface in VLAN 10, so the frame is forwarded out of that single port. Known unicast frames are switched to exactly one port, as determined by the MAC table.
- ✗
Drop the frame because the VLAN does not match
Why it's wrong here
The frame is received on ge-0/0/0 and is tagged with VLAN 10. The destination MAC's forwarding entry is also in VLAN 10, so the frame's VLAN membership is consistent. There is no VLAN mismatch here; a drop would occur only if the ingress VLAN did not match the egress port's VLAN configuration, which is not the case.
- ✗
Forward the frame out of both ge-0/0/1 and ge-0/0/2
Why it's wrong here
The destination MAC address is a unicast address, not a multicast or broadcast address. Forwarding the frame to multiple ports would be appropriate only for BUM (broadcast, unknown unicast, multicast) traffic, where the frame is replicated. Since the MAC table contains a specific entry for this destination on ge-0/0/2, the frame must be sent to that single port only, not to ge-0/0/1 as well.
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 |
Go deeper
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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.