The correct answer is that TI-LFA computes a backup path that is guaranteed to be loop-free and topology independent. This works because TI-LFA leverages segment lists in SR-MPLS or SRv6 to construct a repair path that explicitly avoids the failed link or node, using a post-convergence path that is precomputed and independent of the surrounding network topology. On the Cisco SPCOR / CCNP Service Provider Core 350-501 exam, this concept tests your understanding of how Segment Routing achieves fast convergence without relying on the network’s specific topology, unlike traditional LFA or remote LFA. A common trap is confusing TI-LFA with topology-dependent mechanisms like per-prefix LFA, but the key differentiator is that TI-LFA’s backup path is precomputed using segment lists and works regardless of topology changes. Memory tip: think “TI” for “Topology Independent” — the backup path is always valid, no matter how the network is shaped.
350-501 Networking Practice Question
This 350-501 practice question tests your understanding of networking. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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.
Segment Routing with TI-LFA (Topology Independent Loop-Free Alternate) provides fast convergence. Which statement accurately describes TI-LFA?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
TI-LFA computes a backup path that is guaranteed to be loop-free and topology independent.
TI-LFA computes a backup path using segment lists that are guaranteed to avoid the failed link/node, and it works regardless of the network topology (topology independent). It is based on SR-MPLS or SRv6.
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.
✗
TI-LFA only protects against link failures, not node failures.
Why it's wrong here
TI-LFA can protect against both link and node failures.
✗
TI-LFA uses a pre-computed backup tunnel signaled via RSVP-TE.
Why it's wrong here
TI-LFA is segment routing based, not RSVP.
✓
TI-LFA computes a backup path that is guaranteed to be loop-free and topology independent.
Why this is correct
TI-LFA uses post-convergence path and ensures loop avoidance.
Related concept
Static NAT maps one inside address to one outside address.
✗
TI-LFA requires BFD to detect failures.
Why it's wrong here
BFD can be used but is not mandatory; TI-LFA can rely on IGP convergence.
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.
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.
Networking — This question tests Networking — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: TI-LFA computes a backup path that is guaranteed to be loop-free and topology independent. — TI-LFA computes a backup path using segment lists that are guaranteed to avoid the failed link/node, and it works regardless of the network topology (topology independent). It is based on SR-MPLS or SRv6.
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.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
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Question Discussion
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