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.”
JNCIA-JUNOS Routing Fundamentals Practice Question
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?
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
The loop occurs because the OSPF route (preference 10) is active, pointing a BGP next-hop that causes a recursive loop. By increasing the OSPF route's preference to 175 (higher than BGP's 170), the BGP route becomes active, and if the BGP next-hop is reachable via a non-looping path, the loop stops. Option A is correct. Option B is incorrect because setting next-hop to self does not prevent the OSPF route from being used. Option C is incorrect because a static route would override BGP and would not be received via BGP. Option D is incorrect because route reflection does not address the preference conflict.
Key principle: OSPF neighbour adjacency depends on matching area, hello/dead timers, network type, and authentication — IP reachability alone is not enough.
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
Why this is correct
A higher preference value makes OSPF less preferred than BGP, so the BGP route becomes active and the loop is resolved.
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: OSPF can fail even when IP connectivity looks correct
OSPF neighbour formation depends on matching areas, timers, network type, authentication and passive-interface behaviour. Do not choose an answer only because the devices can ping.
Detailed technical explanation
How to think about this question
OSPF questions usually test the details that control adjacency and route selection. Read the neighbour state, area, router ID and interface configuration before deciding what is wrong.
KKey Concepts to Remember
OSPF neighbours must agree on key parameters.
Router ID selection can affect neighbour relationships and LSDB output.
OSPF cost influences the preferred path.
A route can appear in OSPF information but not become the installed route.
TExam Day Tips
→Check area mismatch first when OSPF adjacency fails.
→Review passive interfaces when a network is advertised but no neighbour forms.
→Use show ip ospf neighbor and show ip route clues carefully.
Key takeaway
OSPF neighbour adjacency depends on matching area, hello/dead timers, network type, and authentication — IP reachability alone is not enough.
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.
What to study next
Got this wrong? Here's your next step.
Review OSPF neighbour requirements — matching area type, hello and dead timers, network type, stub flags, and authentication. Study show ip ospf neighbor states (INIT, 2-WAY, FULL). Then practise related JNCIA-JUNOS OSPF questions on adjacency and route selection.
Routing Fundamentals — This question tests Routing Fundamentals — OSPF neighbours must agree on key parameters..
What is the correct answer to this question?
The correct answer is: Increase the OSPF preference for 10.1.1.0/24 to 175 — The loop occurs because the OSPF route (preference 10) is active, pointing a BGP next-hop that causes a recursive loop. By increasing the OSPF route's preference to 175 (higher than BGP's 170), the BGP route becomes active, and if the BGP next-hop is reachable via a non-looping path, the loop stops. Option A is correct. Option B is incorrect because setting next-hop to self does not prevent the OSPF route from being used. Option C is incorrect because a static route would override BGP and would not be received via BGP. Option D is incorrect because route reflection does not address the preference conflict.
What should I do if I get this JNCIA-JUNOS question wrong?
Review OSPF neighbour requirements — matching area type, hello and dead timers, network type, stub flags, and authentication. Study show ip ospf neighbor states (INIT, 2-WAY, FULL). Then practise related JNCIA-JUNOS OSPF questions on adjacency and route selection.
What is the key concept behind this question?
OSPF neighbours must agree on key parameters.
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