The answer is the low-bandwidth serial link between R1 and R2, which delays EIGRP query packets and causes the active timer to expire, leading to a stuck-in-active (SIA) condition. In EIGRP, when a route goes active, the router sends queries to all neighbors; if a reply is not received within the default three-minute active timer, the neighbor is declared stuck-in-active. In this VRF-Lite scenario, the query propagates from R1 through R2 to R3, but the slow serial link introduces enough delay that R1 never gets the reply in time, triggering SIA. On the Cisco CCNP ENARSI 300-410 exam, this tests your understanding of how query scoping and link characteristics interact in VRF-Lite, with a common trap being to blame R3 or misconfigured timers instead of the physical link. Remember the memory tip: “Slow serial, SIA peril—queries need speed, not a crawl.”
300-410 VRF-Lite Practice Question
This 300-410 practice question tests your understanding of vrf-lite. 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.
Router R1 is running EIGRP in VRF-A with two neighbors: R2 and R3. R2 is a directly connected router, R3 is reachable via R2. The network is experiencing EIGRP stuck-in-active (SIA) routes for prefixes learned from R3. R1 configuration: router eigrp 100, address-family ipv4 vrf VRF-A, network 10.0.0.0. R2 is configured similarly. The link between R1 and R2 is a serial link with low bandwidth. What is the root cause?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The low-bandwidth serial link between R1 and R2 causes EIGRP query packets to be delayed, exceeding the active timer and resulting in SIA.
EIGRP SIA occurs when a query is sent to a neighbor and the reply is not received within the active timer (default 3 minutes). In a VRF-Lite scenario, if the query scope is not limited, the query may propagate to R3 via R2, but if the serial link has low bandwidth or high delay, the query may time out. However, the most common cause in VRF-Lite is that the query is sent to all neighbors, and if one neighbor (R2) does not reply due to a slow link, SIA occurs. The issue is that the query scope includes R2, but the link is slow, causing the active timer to expire.
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.
✓
The low-bandwidth serial link between R1 and R2 causes EIGRP query packets to be delayed, exceeding the active timer and resulting in SIA.
Why this is correct
Correct: Slow link can delay query/reply packets, leading to SIA.
The active timer should be increased to prevent SIA.
Why it's wrong here
Incorrect: While increasing the timer may mask the issue, the root cause is the slow link; the question asks for root cause.
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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 300-410 question in full detail.
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 300-410 OSPF questions on adjacency and route selection.
VRF-Lite — This question tests VRF-Lite — OSPF neighbours must agree on key parameters..
What is the correct answer to this question?
The correct answer is: The low-bandwidth serial link between R1 and R2 causes EIGRP query packets to be delayed, exceeding the active timer and resulting in SIA. — EIGRP SIA occurs when a query is sent to a neighbor and the reply is not received within the active timer (default 3 minutes). In a VRF-Lite scenario, if the query scope is not limited, the query may propagate to R3 via R2, but if the serial link has low bandwidth or high delay, the query may time out. However, the most common cause in VRF-Lite is that the query is sent to all neighbors, and if one neighbor (R2) does not reply due to a slow link, SIA occurs. The issue is that the query scope includes R2, but the link is slow, causing the active timer to expire.
What should I do if I get this 300-410 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 300-410 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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