Quick Answer
The answer is RSVP-TE Fast Reroute (FRR), Topology-Independent LFA (TI-LFA), and LFA. These three are valid methods to provide fast convergence in an MPLS/Segment Routing network because they each pre-compute and pre-install backup paths to achieve sub-50ms failover, bypassing the need for slow IGP reconvergence. TI-LFA, for instance, uses a segment list in the Segment Routing data plane to guarantee a loop-free repair path regardless of topology, while LFA relies on the IGP’s natural loop-free alternates, and RSVP-TE FRR explicitly signals detour or bypass tunnels. On the Cisco SPCOR 350-501 exam, this question tests your ability to distinguish between true fast convergence mechanisms and slower reactive methods like IGP SPF recalculation or BGP PIC—a common trap is confusing LFA with TI-LFA, but remember that TI-LFA is topology-independent and works where LFA fails. Memory tip: “LFA, TI-LFA, and RSVP-TE FRR are the three Rs of fast reroute: Reactive, Reliable, and Reserved.”
This 350-501 practice question tests your understanding of mpls and segment routing. 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.
Which THREE are valid methods to provide fast convergence in an MPLS/Segment Routing network? (Select three.)
BGP Prefix Independent Convergence (PIC)
Why wrong: PIC is for BGP edge convergence, not transport.
Topology-Independent LFA (TI-LFA)
TI-LFA works with SR and provides node/link protection.
Loop-Free Alternate (LFA)
LFA provides link-protection fast reroute.
RSVP-TE Fast Reroute (FRR)
RSVP-TE supports pre-signaled backup tunnels.
IP Fast Reroute (IPFRR)
Why wrong: IPFRR is for native IP, not MPLS.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Topology-Independent LFA (TI-LFA)
B is correct because Topology-Independent LFA (TI-LFA) provides fast convergence in Segment Routing networks by computing a backup path that is guaranteed to be loop-free regardless of the network topology. It leverages the Segment Routing data plane to pre-install a repair path using a segment list, enabling sub-50ms failover without relying on IGP convergence.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
BGP Prefix Independent Convergence (PIC)
Why it's wrong here
PIC is for BGP edge convergence, not transport.
Topology-Independent LFA (TI-LFA)
Why this is correct
TI-LFA works with SR and provides node/link protection.
Related concept
Read the scenario before looking for a memorised answer.
Loop-Free Alternate (LFA)
Why this is correct
LFA provides link-protection fast reroute.
Related concept
Read the scenario before looking for a memorised answer.
RSVP-TE Fast Reroute (FRR)
Why this is correct
RSVP-TE supports pre-signaled backup tunnels.
Related concept
Read the scenario before looking for a memorised answer.
IP Fast Reroute (IPFRR)
Why it's wrong here
IPFRR is for native IP, not MPLS.
Common exam traps
Cisco often tests the distinction between IPFRR (which is IP-layer only) and TI-LFA/LFA/RSVP-TE FRR (which are MPLS/Segment Routing-specific), so candidates mistakenly select IPFRR because it sounds similar to LFA, but it does not apply to MPLS/Segment Routing networks.
Detailed technical explanation
TI-LFA works by computing a post-convergence path and encoding it as a segment list (e.g., adjacency SIDs or node SIDs) that is installed in the forwarding table before a failure occurs. Upon failure, the protecting router immediately switches traffic to the pre-computed segment list, avoiding any IGP reconvergence delay. In real-world deployments, TI-LFA is often combined with Microloop Avoidance to prevent transient loops during IGP convergence after the failure.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
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
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MPLS and Segment Routing — study guide chapter
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FAQ
MPLS and Segment Routing — This question tests MPLS and Segment Routing — Read the scenario before looking for a memorised answer..
The correct answer is: Topology-Independent LFA (TI-LFA) — B is correct because Topology-Independent LFA (TI-LFA) provides fast convergence in Segment Routing networks by computing a backup path that is guaranteed to be loop-free regardless of the network topology. It leverages the Segment Routing data plane to pre-install a repair path using a segment list, enabling sub-50ms failover without relying on IGP convergence.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 25, 2026
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