The correct configuration is to assign the primary static route a lower preference value and the backup a higher preference value. This works because Junos uses the preference metric to select among multiple routes to the same destination; the route with the lowest preference is installed in the forwarding table first. When the primary next-hop at 192.168.1.1 becomes unreachable, the route is withdrawn, and the backup route with the higher preference automatically takes over, providing deterministic failover. On the JNCIA-Junos exam, this concept tests your understanding of static route preference as a tiebreaker for redundancy, often appearing in scenario-based questions where you must avoid the common trap of confusing preference with metric or assuming a higher preference is better. Remember the simple mnemonic: lower preference wins, so the primary gets the lower number to be preferred first.
JNCIA-JUNOS Routing Fundamentals Practice Question
This JNCIA-JUNOS practice question tests your understanding of routing fundamentals. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
An engineer is configuring multiple static routes to the same destination for redundancy. The primary link uses 192.168.1.1 and the backup uses 192.168.2.1. They want the backup to be used only when the primary next-hop is unreachable. Which configuration is correct?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "primary"
Why it matters: Asks for the main purpose or function, not a secondary benefit. Eliminate answers that describe side-effects or partial functions.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Configure the primary with a lower preference and the backup with a higher preference.
Configure the primary with a lower preference and the backup with a higher preference. When the primary is reachable, it is preferred due to lower preference. If it fails, the backup with higher preference becomes active. Option A would not provide deterministic failover. Option C would make backup primary. Option D is not applicable.
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✓
Configure the primary with a lower preference and the backup with a higher preference.
Why this is correct
Lower preference is more preferred; when primary fails, backup takes over.
Clue confirmation
The clue word "primary" in the question point toward this answer.
Related concept
Static NAT maps one inside address to one outside address.
✗
Configure the primary with a higher preference and the backup with a lower preference.
Why it's wrong here
This would make the backup the primary, opposite of the requirement.
✗
Configure two static routes with equal preferences; the active route will be chosen based on next-hop IP.
Why it's wrong here
Equal preferences would cause both to be installed, but failover behavior is not guaranteed as expected.
✗
Configure the routes with the same preference but use a policy to set metric.
Why it's wrong here
Metric is not used for static route selection; preference is the only factor.
Common exam traps
Common exam trap: NAT rules depend on direction and matching traffic
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Detailed technical explanation
How to think about this question
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
KKey Concepts to Remember
Static NAT maps one inside address to one outside address.
PAT allows many inside hosts to share one public address using ports.
Inside local and inside global describe the private and translated addresses.
NAT ACLs identify traffic for translation, not always security filtering.
TExam Day Tips
→Identify inside and outside interfaces first.
→Check whether the scenario needs static NAT, dynamic NAT or PAT.
→Do not confuse NAT matching ACLs with normal packet-filtering intent.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Real-world example
How this comes up in practice
A small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
What to study next
Got this wrong? Here's your next step.
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related JNCIA-JUNOS NAT questions on configuration and troubleshooting.
Routing Fundamentals — This question tests Routing Fundamentals — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: Configure the primary with a lower preference and the backup with a higher preference. — Configure the primary with a lower preference and the backup with a higher preference. When the primary is reachable, it is preferred due to lower preference. If it fails, the backup with higher preference becomes active. Option A would not provide deterministic failover. Option C would make backup primary. Option D is not applicable.
What should I do if I get this JNCIA-JUNOS question wrong?
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related JNCIA-JUNOS NAT questions on configuration and troubleshooting.
Are there clue words in this question I should notice?
Yes — watch for: "primary". Asks for the main purpose or function, not a secondary benefit. Eliminate answers that describe side-effects or partial functions.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
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