The answer is that the RSVP bandwidth is not configured on the interface or is set to 0. This is because MPLS-TE RSVP admission control checks the interface’s configured bandwidth pool before allowing a Label Switched Path (LSP) to reserve resources; even if the physical link has ample capacity, the headend router will reject the reservation if the `rsvp bandwidth` command is missing or set to zero, as the admission control process has no pool from which to allocate. On the Cisco SPCOR 350-501 exam, this scenario tests your understanding of RSVP-TE resource management, often appearing as a trick where candidates assume a bandwidth issue is due to congestion rather than a missing interface-level configuration. A common trap is overlooking that RSVP bandwidth must be explicitly enabled on every interface participating in traffic engineering, separate from the interface’s actual speed. Memory tip: “No RSVP pool means no LSP—check the interface, not the link.”
350-501 Architecture Practice Question
This 350-501 practice question tests your understanding of architecture. 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.
An MPLS Traffic Engineering LSP fails to establish. The RSVP signaling shows 'PathErr: Admission Control Failure'. The link has sufficient bandwidth but the headend reports a lack of resources. What is the most likely cause?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The RSVP bandwidth is not configured on the interface or is set to 0
Admission control in RSVP-TE uses bandwidth constraints either per tunnel or per interface. A common misconfiguration is not reserving global pool bandwidth under the interface. The headend could be misconfiguring the bandwidth request, but the error is at the interface level under RSVP. The most common fix is enabling bandwidth reservation under the interface.
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
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 tunnel is requesting more bandwidth than available on any path
Why it's wrong here
The problem states the link has sufficient bandwidth.
✗
The MPLS forwarding table is corrupted
Why it's wrong here
Corruption would cause label lookup failures, not RSVP signaling.
✗
The headend router does not have the correct destination address
Why it's wrong here
Destination address error would cause no path, not admission control failure.
✓
The RSVP bandwidth is not configured on the interface or is set to 0
Why this is correct
Without 'ip rsvp bandwidth' command on the interface, RSVP cannot allocate resources.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Static NAT maps one inside address to one outside address.
✗
The LSP is configured with a strict explicit path that is impossible
Why it's wrong here
Explicit path failure would show a different error like 'No route to destination'.
Common exam traps
Common exam trap: NAT rules depend on direction and matching traffic
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Trap categories for this question
Command / output trap
Explicit path failure would show a different error like 'No route to destination'.
Detailed technical explanation
How to think about this question
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
KKey Concepts to Remember
Static NAT maps one inside address to one outside address.
PAT allows many inside hosts to share one public address using ports.
Inside local and inside global describe the private and translated addresses.
NAT ACLs identify traffic for translation, not always security filtering.
TExam Day Tips
→Identify inside and outside interfaces first.
→Check whether the scenario needs static NAT, dynamic NAT or PAT.
→Do not confuse NAT matching ACLs with normal packet-filtering intent.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Real-world example
How this comes up in practice
A small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
What to study next
Got this wrong? Here's your next step.
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related 350-501 NAT questions on configuration and troubleshooting.
Architecture — This question tests Architecture — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: The RSVP bandwidth is not configured on the interface or is set to 0 — Admission control in RSVP-TE uses bandwidth constraints either per tunnel or per interface. A common misconfiguration is not reserving global pool bandwidth under the interface. The headend could be misconfiguring the bandwidth request, but the error is at the interface level under RSVP. The most common fix is enabling bandwidth reservation under the interface.
What should I do if I get this 350-501 question wrong?
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related 350-501 NAT questions on configuration and troubleshooting.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
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