The answer is that LDP will form adjacencies over both interfaces and distribute labels for all routes in the routing table. This occurs because the `mpls ip` command under each interface enables LDP label distribution on those links, while the OSPF wildcard mask `0.255.255.255` covers both subnets, ensuring all routes learned via OSPF are present in the routing table for LDP to label. On the ENCOR 350-401 exam, this configuration tests your understanding that LDP operates independently of the IGP’s network statement—LDP labels every route in the routing table, not just those in OSPF’s `network` command. A common trap is assuming LDP only labels OSPF routes matching the wildcard; in reality, LDP labels all routes, including connected and static, unless filtered. Remember the memory tip: “LDP labels the whole table, not just the OSPF net statement.”
350-401 MPLS Practice Question
This 350-401 practice question tests your understanding of mpls. 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.
interface GigabitEthernet0/1
ip address 10.1.1.1 255.255.255.0
mpls ip
!
interface GigabitEthernet0/2
ip address 10.2.2.1 255.255.255.0
mpls ip
!
router ospf 1
network 10.0.0.0 0.255.255.255 area 0
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
LDP will form adjacencies over both interfaces and distribute labels for all routes in the routing table.
LDP is enabled on both interfaces, but OSPF is configured with a wildcard that includes both subnets. LDP will form adjacencies and distribute labels for all OSPF routes.
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.
✓
LDP will form adjacencies over both interfaces and distribute labels for all routes in the routing table.
Why this is correct
Correct. LDP adjacencies are formed on interfaces where LDP is enabled, and labels are distributed for all routes.
Only OSPF routes will receive labels; static routes are ignored by LDP.
Why it's wrong here
Incorrect. LDP distributes labels for all routes in the routing table by default.
✗
LDP will only form an adjacency on GigabitEthernet0/1 because it is the first interface configured.
Why it's wrong here
Incorrect. LDP forms adjacencies on all interfaces where it is enabled.
✗
The configuration will fail because OSPF and LDP are not compatible on the same interface.
Why it's wrong here
Incorrect. OSPF and LDP are compatible and commonly used together.
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 350-401 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 350-401 OSPF questions on adjacency and route selection.
MPLS — This question tests MPLS — OSPF neighbours must agree on key parameters..
What is the correct answer to this question?
The correct answer is: LDP will form adjacencies over both interfaces and distribute labels for all routes in the routing table. — LDP is enabled on both interfaces, but OSPF is configured with a wildcard that includes both subnets. LDP will form adjacencies and distribute labels for all OSPF routes.
What should I do if I get this 350-401 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 350-401 OSPF questions on adjacency and route selection.
What is the key concept behind this question?
OSPF neighbours must agree on key parameters.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. interface GigabitEthernet0/1
ip address 10.1.1.1 255.255.255.0
mpls ip
!
interface GigabitEthernet0/2
ip address 10.2.2.1 255.255.255.0
mpls ip
!
router ospf 1
network 10.0.0.0 0.255.255.255 area 0
!
router ldp
interface GigabitEthernet0/1
!
What is the effect of this configuration?
medium
✓ A.LDP will only form an adjacency over GigabitEthernet0/1; no label exchange occurs on GigabitEthernet0/2.
B.LDP will automatically enable on GigabitEthernet0/2 because MPLS is enabled there.
C.The configuration will fail because LDP must be enabled on all MPLS interfaces.
D.OSPF will automatically enable LDP on all interfaces in area 0.
Why A: LDP is only enabled on GigabitEthernet0/1, not on GigabitEthernet0/2. This means LDP will not form an adjacency over GigabitEthernet0/2, and MPLS forwarding may be incomplete.
Variation 2. interface GigabitEthernet0/1
ip address 10.1.1.1 255.255.255.0
mpls ip
mpls label protocol ldp
!
router ospf 1
network 10.1.1.0 0.0.0.255 area 0
!
router ldp
interface GigabitEthernet0/1
!
What is the effect of this configuration?
medium
✓ A.MPLS forwarding is enabled on GigabitEthernet0/1, and LDP will distribute labels for all routes in the routing table.
B.Only OSPF routes are labeled; static routes are excluded from LDP label distribution.
C.The 'mpls label protocol ldp' command is redundant because LDP is the default.
D.The configuration will fail because 'router ldp' requires an LDP router-id to be set.
Why A: The configuration enables MPLS forwarding and LDP on the interface, with OSPF providing IGP reachability. LDP will distribute labels for prefixes learned via OSPF.
Variation 3. interface GigabitEthernet0/1
ip address 10.1.1.1 255.255.255.0
mpls ip
mpls label protocol tdp
!
router ospf 1
network 10.1.1.0 0.0.0.255 area 0
!
router ldp
interface GigabitEthernet0/1
!
Which statement about this configuration is true?
medium
✓ A.The interface will use TDP for label distribution, ignoring the LDP configuration under router ldp.
B.The router will use LDP because the global configuration overrides the interface command.
C.Both TDP and LDP will be used simultaneously on the interface.
D.The configuration will fail because TDP is not supported on this platform.
Why A: The interface is configured with TDP (Cisco proprietary) while the router is configured for LDP (standard). This mismatch will prevent label exchange.
Last reviewed: Jun 18, 2026
Question Discussion
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