The answer is that the OSPF network statement uses an incorrect wildcard mask. This is correct because the wildcard mask 0.0.0.0 matches only the single host IP 10.1.1.1, but the interface is configured with a /30 prefix, which requires a wildcard mask of 0.0.0.3 to include the entire subnet. Without the proper wildcard mask, OSPF fails to advertise the correct network, breaking CE-to-PE routing in the MPLS VPN environment. On the Cisco SPCOR 350-501 exam, this scenario tests your understanding of how OSPF wildcard mask configuration directly impacts neighbor discovery and route advertisement in service provider networks. A common trap is confusing the host mask 0.0.0.0 with the subnet mask needed for point-to-point links; remember that OSPF wildcard masks are the inverse of the subnet mask, not the subnet mask itself. A useful memory tip is to subtract the subnet mask from 255.255.255.255 to get the correct wildcard—for a /30, 255.255.255.252 becomes 0.0.0.3.
350-501 Architecture Practice Question
This 350-501 practice question tests your understanding of architecture. 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.
Refer to the exhibit. The router is configured as a PE router in an MPLS VPN network. Which option correctly identifies a configuration error that would prevent proper operation?
The neighbor remote-as should be the same AS number for iBGP
Why wrong: The neighbor is in a different AS, so eBGP is correct.
B
The interface lacks the 'mpls ip' command
Why wrong: The exhibit does not show MPLS configuration, but the question asks for an error shown in the exhibit; the absence of 'mpls ip' is not visible.
C
The OSPF network statement uses an incorrect wildcard mask
The wildcard mask 0.255.255.255 is too broad and does not match the /30 prefix correctly.
D
The BGP network statement does not match the interface prefix
Why wrong: The BGP network command can specify a more specific prefix than the interface; it is not an error.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The OSPF network statement uses an incorrect wildcard mask
Option C is correct because the OSPF network statement uses a wildcard mask of 0.0.0.0, which matches only the exact IP address 10.1.1.1, but the interface has a /30 prefix (255.255.255.252), so the correct wildcard mask should be 0.0.0.3 to include the entire subnet. This misconfiguration prevents OSPF from advertising the correct network, breaking MPLS VPN CE-to-PE routing.
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.
✗
The neighbor remote-as should be the same AS number for iBGP
Why it's wrong here
The neighbor is in a different AS, so eBGP is correct.
✗
The interface lacks the 'mpls ip' command
Why it's wrong here
The exhibit does not show MPLS configuration, but the question asks for an error shown in the exhibit; the absence of 'mpls ip' is not visible.
✓
The OSPF network statement uses an incorrect wildcard mask
Why this is correct
The wildcard mask 0.255.255.255 is too broad and does not match the /30 prefix correctly.
Related concept
Read the scenario before looking for a memorised answer.
✗
The BGP network statement does not match the interface prefix
Why it's wrong here
The BGP network command can specify a more specific prefix than the interface; it is not an error.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the distinction between OSPF wildcard masks and subnet masks, where candidates mistakenly think any wildcard mask that includes the interface IP is sufficient, but the mask must match the subnet exactly for OSPF to advertise the correct network.
Trap categories for this question
Command / output trap
The exhibit does not show MPLS configuration, but the question asks for an error shown in the exhibit; the absence of 'mpls ip' is not visible.
Detailed technical explanation
How to think about this question
In OSPF, the network statement uses a wildcard mask to define which interfaces participate in the OSPF process; a /30 prefix (255.255.255.252) requires a wildcard mask of 0.0.0.3 to match all four addresses in the subnet. Using 0.0.0.0 matches only the specific IP, which is valid for loopbacks but not for point-to-point links, causing OSPF to fail to advertise the connected subnet to the CE router. This is a common misconfiguration in MPLS VPN setups where OSPF is used as the PE-CE routing protocol, as the PE must advertise the correct prefix to establish the VRF route.
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.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Architecture — This question tests Architecture — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The OSPF network statement uses an incorrect wildcard mask — Option C is correct because the OSPF network statement uses a wildcard mask of 0.0.0.0, which matches only the exact IP address 10.1.1.1, but the interface has a /30 prefix (255.255.255.252), so the correct wildcard mask should be 0.0.0.3 to include the entire subnet. This misconfiguration prevents OSPF from advertising the correct network, breaking MPLS VPN CE-to-PE routing.
What should I do if I get this 350-501 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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Question Discussion
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