- A
Configure per-packet load balancing under the interface
Why wrong: Per-packet load balancing is not standard for routing protocols in JunOS; per-flow is typical.
- B
Add 'multipath' under 'routing-options' for OSPF
'multipath' enables ECMP, which allows multiple equal-cost routes to be used.
- C
Define a load-balancing hash-key including Layer 4 information
Why wrong: Hash-key configuration is optional and does not enable ECMP itself.
- D
Set a higher preference on one path to force ECMP
Why wrong: Higher preference makes the route less preferred, not equal.
Question 193 of 514
JNCIA-JUNOS Routing Fundamentals Practice Question
This JNCIA-JUNOS practice question tests your understanding of routing fundamentals. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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.
A network has two equal-cost OSPF paths to 192.168.1.0/24. The engineer wants to enable per-flow load balancing. Which configuration element is required?
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
✓
Add 'multipath' under 'routing-options' for OSPF
Option B is correct because per-flow load balancing in Junos requires the 'multipath' statement under 'routing-options' to enable ECMP (Equal-Cost Multipath) for OSPF. Without this, Junos will only install a single best path even if multiple equal-cost routes exist. Once 'multipath' is configured, the system automatically uses per-flow load balancing based on the default hash key (source/destination IP and optionally Layer 4 ports).
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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 per-packet load balancing under the interface
Why it's wrong here
Per-packet load balancing is not standard for routing protocols in JunOS; per-flow is typical.
- ✓
Add 'multipath' under 'routing-options' for OSPF
Why this is correct
'multipath' enables ECMP, which allows multiple equal-cost routes to be used.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Define a load-balancing hash-key including Layer 4 information
Why it's wrong here
Hash-key configuration is optional and does not enable ECMP itself.
- ✗
Set a higher preference on one path to force ECMP
Why it's wrong here
Higher preference makes the route less preferred, not equal.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume OSPF automatically performs ECMP load balancing in Junos, but it requires the explicit 'multipath' configuration, unlike Cisco IOS where OSPF ECMP is enabled by default when equal-cost paths exist.
Detailed technical explanation
How to think about this question
Under the hood, Junos uses a hash-based algorithm for per-flow load balancing, where the hash is computed from fields in the packet header (e.g., source/destination IP, protocol, and optionally ports) to select the next hop. The 'multipath' statement is required because OSPF in Junos does not automatically install multiple equal-cost routes into the forwarding table; it must be explicitly enabled at the routing-options level. A real-world scenario where this matters is in data center fabrics where multiple equal-cost links exist between leaf and spine switches—without 'multipath', only one link would be utilized, wasting bandwidth.
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A network engineer at a university connects two campus buildings via a fibre link. Both routers run OSPF, but no adjacency forms — even though both routers can ping each other. The engineer finds one router is in area 0 and the other in area 1. OSPF adjacency requires matching area numbers, hello/dead timers, and network type. IP reachability alone is not enough.
Visual reference
Quick reference
Routing Protocol Comparison
| Protocol | Metric | Max Hops | Algorithm | Type |
|---|---|---|---|---|
| RIP v2 | Hop count | 15 | Bellman-Ford | Distance vector |
| OSPF | Cost (bandwidth) | Unlimited | Dijkstra (SPF) | Link state |
| EIGRP | Composite metric | Unlimited | DUAL | Hybrid |
| IS-IS | Cost | Unlimited | Dijkstra | Link state |
| BGP | Policy / attributes | Unlimited | Path vector | Path vector |
RIP's 15-hop limit makes it unsuitable for large networks. OSPF and EIGRP dominate modern enterprise deployments.
What to study next
Got this wrong? Here's your next step.
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FAQ
Questions learners often ask
What does this JNCIA-JUNOS question test?
Routing Fundamentals — This question tests Routing Fundamentals — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Add 'multipath' under 'routing-options' for OSPF — Option B is correct because per-flow load balancing in Junos requires the 'multipath' statement under 'routing-options' to enable ECMP (Equal-Cost Multipath) for OSPF. Without this, Junos will only install a single best path even if multiple equal-cost routes exist. Once 'multipath' is configured, the system automatically uses per-flow load balancing based on the default hash key (source/destination IP and optionally Layer 4 ports).
What should I do if I get this JNCIA-JUNOS question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jul 4, 2026
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