JN0-106 Networking Fundamentals Practice Question

Exhibit

Refer to the exhibit.

```
user@switch> show configuration interfaces ge-0/0/1
unit 0 {
    family ethernet-switching {
        port-mode access;
        vlan {
            members VLAN10;
        }
    }
}

user@switch> show vlans
VLAN name           Status    Ports
VLAN10              Up        ge-0/0/1, ge-0/0/2
VLAN20              Up        ge-0/0/3
```

Refer to the exhibit. A host connected to ge-0/0/1 cannot reach a host connected to ge-0/0/2 even though both are in VLAN10. What is the most likely cause?

⚠ Common exam trap

Many candidates assume VLAN membership alone guarantees IP connectivity, overlooking the fact that IP communication requires the hosts to be in the same IP subnet or have a router to forward traffic between subnets.

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

✓

The hosts are configured with IP addresses on different subnets.

Although both hosts are in the same VLAN and can communicate at Layer 2 (MAC addresses), IP communication requires them to be on the same IP subnet. If the hosts have IP addresses on different subnets, they will attempt to use a default gateway for routing. Without a router or IRB interface configured, the traffic cannot be delivered, leading to unreachability.

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

✗
VLAN10 is not defined in the global VLAN configuration.
Why it's wrong here
The exhibit shows VLAN10 listed with its member interfaces and an active status, which proves VLAN10 is defined at the [edit vlans] hierarchy. A VLAN only appears in the output of operational commands like 'show vlans' when it is configured. Since VLAN10 is active, a missing global VLAN definition cannot be the cause of the connectivity failure.
✓
The hosts are configured with IP addresses on different subnets.
Why this is correct
They can't communicate at Layer 2? Actually Layer 2 doesn't care about IP. So this is tricky. Actually within same VLAN, IP subnet must match for Layer 3, but Layer 2 should work. However if hosts are on different subnets, they need a router. But the question says 'cannot reach' - likely they try to ping. If on different subnets, they need default gateway. So the most likely cause is they are on different subnets and no gateway. Alternatively, the switch might have port security. But given typical JNCIA, this is plausible.
✗
An IRB interface for VLAN10 is not configured.
Why it's wrong here
An IRB (integrated routing and bridging) interface provides a Layer 3 gateway for a VLAN, enabling routing between VLANs or to other subnets. For two hosts on the same VLAN and the same IP subnet, communication is purely a Layer 2 broadcast and MAC-learning process, so an IRB is unnecessary. Even if the hosts were on different subnets, an IRB alone would not help unless the hosts are configured with that IRB as their default gateway.
✗
The interface ge-0/0/2 is configured as a trunk port.
Why it's wrong here
On Junos, a trunk port can explicitly include VLAN10 in its 'vlan members' list, so the port would still forward VLAN10 frames. The exhibit shows ge-0/0/2 as a member of VLAN10, which is consistent with either an access port or a trunk whose allowed list contains VLAN10. A trunk port is not inherently incompatible with Layer 2 connectivity in VLAN10; the port's membership matters more than its mode, so this is not the root cause.

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

JN0-106 Networking Fundamentals Practice Question

Exhibit

Why each option matters

Option-by-option breakdown

Access Control Model Comparison

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