The root cause is the symmetric route-target import/export configuration, which creates a full bidirectional route leak between the BLUE and RED VRFs. When both VRFs import each other’s export targets, every route from one VRF is automatically leaked into the other, allowing unintended reachability—like a ping from BLUE to 10.2.2.2 succeeding. This misconfiguration is a classic trap on the Cisco CCNP ENARSI 300-410 exam, testing your understanding that route-target statements control MPLS VPN route distribution, not just VRF membership. Many candidates mistakenly think separate OSPF processes isolate the VRFs, but route-targets override that isolation. The fix is to apply a route-map on the import or export statement to filter specific prefixes, or to use unidirectional target values. Remember the memory tip: “Symmetric targets leak everything; asymmetric or filtered targets keep control.”
300-410 OSPF Troubleshooting (v2/v3) Practice Question
This 300-410 practice question tests your understanding of ospf troubleshooting (v2/v3). 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.
VRF route leaking between two VRFs is causing unexpected reachability to a sensitive subnet. Router R1 has the following relevant configuration: vrf definition BLUE rd 100:1 ! address-family ipv4 route-target export 100:1 route-target import 100:2 vrf definition RED rd 100:2 ! address-family ipv4 route-target export 100:2 route-target import 100:1 interface GigabitEthernet0/0 vrf forwarding BLUE ip address 10.1.1.1 255.255.255.0 interface GigabitEthernet0/1 vrf forwarding RED ip address 10.2.2.1 255.255.255.0 router ospf 1 vrf BLUE network 10.1.1.0 0.0.0.255 area 0 router ospf 2 vrf RED network 10.2.2.0 0.0.0.255 area 0 A ping from a host in BLUE VRF to 10.2.2.2 (RED VRF) succeeds, but it should not. 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
✓
Route-target import/export is symmetric, causing full route exchange; use route-map to filter.
The route-target import/export configuration is bidirectional, causing full route leaking between VRFs. This allows hosts in BLUE to reach RED subnets. The correct fix is to use import/export only for specific prefixes or use route-maps to control leaking.
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.
✓
Route-target import/export is symmetric, causing full route exchange; use route-map to filter.
Why this is correct
Both VRFs import each other's routes, so all routes are leaked. Route-maps can restrict which prefixes are imported.
The OSPF process IDs are different; they should be the same for route leaking.
Why it's wrong here
OSPF process IDs are local; route leaking is via VRF, not OSPF.
✗
The network commands are missing the vrf keyword; add vrf BLUE/RED.
Why it's wrong here
The network commands are under the VRF OSPF process, so correct.
✗
The interfaces are in the wrong VRF; move GigabitEthernet0/1 to BLUE.
Why it's wrong here
Interfaces are correctly assigned; the issue is route leaking.
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.
Trap categories for this question
Command / output trap
The network commands are under the VRF OSPF process, so correct.
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.
OSPF Troubleshooting (v2/v3) — This question tests OSPF Troubleshooting (v2/v3) — OSPF neighbours must agree on key parameters..
What is the correct answer to this question?
The correct answer is: Route-target import/export is symmetric, causing full route exchange; use route-map to filter. — The route-target import/export configuration is bidirectional, causing full route leaking between VRFs. This allows hosts in BLUE to reach RED subnets. The correct fix is to use import/export only for specific prefixes or use route-maps to control leaking.
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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