The answer is enabling TI-LFA on all IS-IS interfaces, as this design choice ensures sub-50ms convergence in a Segment Routing network without relying on any signaling protocol beyond the IGP. TI-LFA, or Topology Independent Loop-Free Alternate, precomputes backup paths using only the IGP’s link-state database, guaranteeing fast reroute even during node failures by leveraging the SR-MPLS data plane to steer traffic around the fault. On the Cisco SPCOR 350-501 exam, this question tests your understanding that TI-LFA is the only mechanism that provides both topology independence and signaling-free protection, contrasting with RSVP-TE or LDP which require explicit signaling or tunnel state. A common trap is confusing BFD’s fast detection role with actual path protection—BFD must be paired with a repair mechanism like TI-LFA. Memory tip: TI-LFA is “topology independent” because it works even when the backup path is not a simple loop-free alternate, and it uses only the IGP, so think “TI-LFA = IGP-only, no extra signaling.”
350-501 Architecture Practice Question
This 350-501 practice question tests your understanding of architecture. 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.
A network architect is designing a Segment Routing (SR) network for a service provider with a requirement for fast convergence upon node failure. The network uses IS-IS as the IGP with segment routing extensions. Which design choice BEST ensures that the network can achieve sub-50ms convergence without relying on any signaling protocol beyond the IGP?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "best"
Why it matters: Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Enable TI-LFA (Topology Independent Loop-Free Alternate) on all ISIS interfaces
Option A is correct because TI-LFA (Topology Independent Loop-Free Alternate) calculates backup paths based solely on IGP and does not require additional signaling. Option B is wrong because RSVP-TE requires TE tunnels and signaling. Option C is wrong because LDP is a separate signaling protocol. Option D is wrong because BFD can be used for fast detection but does not provide a backup path itself; it must be combined with a protection mechanism.
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.
✗
Deploy BFD with static routes for fast detection
Why it's wrong here
BFD only detects failure, does not provide backup path.
✗
Configure RSVP-TE with Fast Reroute on all label-switched paths
Why it's wrong here
RSVP-TE requires TE tunnels and signaling, adding complexity.
✓
Enable TI-LFA (Topology Independent Loop-Free Alternate) on all ISIS interfaces
Why this is correct
TI-LFA provides fast reroute without additional protocols, using SR-MPLS data plane.
Clue confirmation
The clue word "best" in the question point toward this answer.
Related concept
Static NAT maps one inside address to one outside address.
✗
Use LDP with LDP FRR and path protection
Why it's wrong here
LDP is a separate protocol; SR environment avoids LDP for simplicity.
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.
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: Enable TI-LFA (Topology Independent Loop-Free Alternate) on all ISIS interfaces — Option A is correct because TI-LFA (Topology Independent Loop-Free Alternate) calculates backup paths based solely on IGP and does not require additional signaling. Option B is wrong because RSVP-TE requires TE tunnels and signaling. Option C is wrong because LDP is a separate signaling protocol. Option D is wrong because BFD can be used for fast detection but does not provide a backup path itself; it must be combined with a protection mechanism.
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: "best". Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
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 →
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
This 350-501 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 350-501 exam.
Question Discussion
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
Sign in to join the discussion.