- A
Increase the OSPF preference for 10.1.1.0/24 to 175
A higher preference value makes OSPF less preferred than BGP, so the BGP route becomes active and the loop is resolved.
- B
Add a static route for 10.1.1.0/24 with next-hop 10.2.2.2
Why wrong: A static route would become active but would not be advertised via BGP, defeating the purpose.
- C
Configure 'set protocol bgp group internal-mesh local-address 10.2.2.2' to set next-hop to self
Why wrong: Changing next-hop does not affect which route is active; the OSPF route would still be preferred.
- D
Use route reflection to break the loop
Why wrong: Route reflection reduces IBGP peers but does not resolve the route selection conflict.
Question 309 of 514
How to Stop a Routing Loop Between IBGP and OSPF: Increase the OSPF Route Preference
This JNCIA-JUNOS practice question tests your understanding of routing fundamentals. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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.
Two routers running IBGP with full mesh have a routing loop for prefix 10.1.1.0/24. Both routers have an IBGP route (preference 170) for the prefix with next-hop 10.2.2.2, and an OSPF route (preference 10) for the same prefix. The OSPF next-hop on each router points to the other router's loopback interface. Which action should be taken to stop the loop while preserving BGP route advertisement?
Quick Answer
The correct answer is to increase the OSPF route preference for 10.1.1.0/24 to 175. This stops the routing loop because the OSPF route, with a default preference of 10, is currently active and its next-hop points to the other router’s loopback, creating a recursive dependency that cycles between the two IBGP peers. By raising the OSPF preference above IBGP’s 170, the BGP route becomes the active route, and as long as the BGP next-hop is reachable via a non-looping path, the loop is broken while BGP advertisement continues. On the JNCIA-Junos exam, this scenario tests your understanding of route preference as a tiebreaker between protocols and how recursive next-hop resolution can cause loops when a lower-preference IGP route points back into the BGP topology. A common trap is assuming next-hop-self or route reflection fixes the underlying preference conflict. Memory tip: think “OSPF is too eager at 10—bump it past BGP’s 170 to break the loop.”
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
✓
Increase the OSPF preference for 10.1.1.0/24 to 175
Option A is correct because increasing the OSPF preference for 10.1.1.0/24 to 175 makes the IBGP route (preference 170) more preferred than the OSPF route. This breaks the routing loop where each router's OSPF route points to the other's loopback, while preserving the IBGP route advertisement. The loop occurs because both routers prefer the OSPF route (preference 10) over IBGP (preference 170), causing traffic to bounce between them.
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.
- ✓
Increase the OSPF preference for 10.1.1.0/24 to 175
- ✗
Add a static route for 10.1.1.0/24 with next-hop 10.2.2.2
Why it's wrong here
A static route would become active but would not be advertised via BGP, defeating the purpose.
- ✗
Configure 'set protocol bgp group internal-mesh local-address 10.2.2.2' to set next-hop to self
Why it's wrong here
Changing next-hop does not affect which route is active; the OSPF route would still be preferred.
- ✗
Use route reflection to break the loop
Why it's wrong here
Route reflection reduces IBGP peers but does not resolve the route selection conflict.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates may think the loop is caused by BGP next-hop behavior or session configuration, rather than recognizing it as a route preference issue where OSPF's lower preference overrides IBGP, leading to a forwarding loop between the two routers.
Detailed technical explanation
How to think about this question
In JUNOS, route preference (administrative distance) determines which route is installed in the forwarding table when multiple protocols provide routes to the same prefix. OSPF has a default preference of 10, while IBGP has 170. By increasing OSPF's preference to 175, the IBGP route becomes the active route, breaking the loop. This is a common technique in multi-protocol environments to control route selection without altering protocol advertisements.
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
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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: Increase the OSPF preference for 10.1.1.0/24 to 175 — Option A is correct because increasing the OSPF preference for 10.1.1.0/24 to 175 makes the IBGP route (preference 170) more preferred than the OSPF route. This breaks the routing loop where each router's OSPF route points to the other's loopback, while preserving the IBGP route advertisement. The loop occurs because both routers prefer the OSPF route (preference 10) over IBGP (preference 170), causing traffic to bounce between them.
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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