JN0-106 Routing Fundamentals Practice Question
Exhibit
Refer to the exhibit.
```
user@router> show route protocol static
inet.0: 5 destinations, 5 routes (5 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both
0.0.0.0/0 *[Static/5] 00:10:00, metric2 0
> to 192.168.1.1 via ge-0/0/0.0
10.0.0.0/8 *[Static/5] 00:05:00, metric2 0
> to 10.0.0.1 via ge-0/0/1.0
172.16.0.0/16 *[Static/5] 00:02:00, metric2 0
> to 172.16.0.1 via ge-0/0/2.0
```Refer to the exhibit. The router has three static routes configured. Which route will be used to forward a packet destined to 172.16.1.100?
⚠ Common exam trap
Watch out — candidates often assume a default route will always be used as a catch-all, but they forget that a more specific static route (like 172.16.0.0/16) will take precedence over the default route for matching destinations.
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 static route to 172.16.0.0/16
The router will use the most specific matching route for the destination 172.16.1.100. The static route to 172.16.0.0/16 has a prefix length of 16, which is more specific than the default route (0.0.0.0/0) and the route to 10.0.0.0/8 (which does not match the destination). Therefore, the route to 172.16.0.0/16 is selected based on the longest-prefix-match rule.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The default route (0.0.0.0/0)
Why it's wrong here
The default route (0.0.0.0/0) has a prefix length of 0, making it the least specific match. For destination 172.16.1.100, the static route to 172.16.0.0/16 has a longer prefix length and is therefore preferred by Junos's longest-prefix-match logic. The default route is only consulted when no other route with a more specific prefix exists.
- ✗
The router will drop the packet.
Why it's wrong here
A router drops a packet only when no matching route is found or the selected next hop is unreachable. Here, the destination 172.16.1.100 matches the static route to 172.16.0.0/16, which has a valid next hop, so the packet is forwarded rather than discarded. The existence of a valid matching route invalidates the drop scenario.
- ✗
The static route to 10.0.0.0/8
Why it's wrong here
The static route to 10.0.0.0/8 is not a candidate because 172.16.1.100 is not within that prefix range — it begins with 172, not 10. The address belongs to the 172.16.0.0/12 block, and more specifically to the configured 172.16.0.0/16 route. A route can only be selected if the destination address is mathematically contained within the route's prefix.
- ✓
The static route to 172.16.0.0/16
Why this is correct
The destination 172.16.1.100 lies exactly within the 172.16.0.0/16 network, and this is the most specific static route matching the destination. Junos applies the longest-prefix-match rule, so this route is selected to forward the packet toward its next hop. No other static route in the exhibit is more specific, making this the correct forwarding entry.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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