nerdexam
Cisco

352-001 · Question #550

Which two options are Loop-Free Alternate design considerations? (Choose two)

The correct answer is B. Backup coverage and effectiveness is dependent on the network topology E. It can impact SLA-sensitive appliance by routing traffic to low bandwidth links while IGP. Loop-Free Alternate (LFA) provides pre-computed IP Fast Reroute backup paths, but its coverage is topology-dependent and it can cause SLA issues by sending traffic over suboptimal links during convergence.

Layer 3 Control Plane

Question

Which two options are Loop-Free Alternate design considerations? (Choose two)

Options

  • AMPLS TE must be enabled because it is used for building the backup paths
  • BBackup coverage and effectiveness is dependent on the network topology
  • CIt can simplify the capacity planning by matching the backup path with the post-convergence path
  • DIt provides an optional backup path by avoiding low bandwidth and edge links
  • EIt can impact SLA-sensitive appliance by routing traffic to low bandwidth links while IGP

How the community answered

(30 responses)
  • A
    10% (3)
  • B
    57% (17)
  • C
    27% (8)
  • D
    7% (2)

Why each option

Loop-Free Alternate (LFA) provides pre-computed IP Fast Reroute backup paths, but its coverage is topology-dependent and it can cause SLA issues by sending traffic over suboptimal links during convergence.

AMPLS TE must be enabled because it is used for building the backup paths

MPLS TE is not required for LFA - LFA is an IGP-native IP Fast Reroute mechanism that uses SPF calculations and does not rely on MPLS TE tunnels for building backup paths.

BBackup coverage and effectiveness is dependent on the network topologyCorrect

LFA backup coverage is entirely dependent on whether a neighboring node offers a loop-free alternate path per the inequality check defined in RFC 5286. In topologies with few alternate paths, many prefixes will have no LFA coverage, making topology a primary design constraint.

CIt can simplify the capacity planning by matching the backup path with the post-convergence path

LFA does not simplify capacity planning - because the backup path often differs from the post-convergence path, capacity planning must account for two separate traffic distributions, increasing complexity.

DIt provides an optional backup path by avoiding low bandwidth and edge links

LFA does not inherently avoid low-bandwidth or edge links - the backup next-hop is selected purely based on the loop-free inequality check, with no automatic exclusion of low-bandwidth interfaces.

EIt can impact SLA-sensitive appliance by routing traffic to low bandwidth links while IGPCorrect

During IGP convergence, LFA reroutes traffic to a pre-computed backup path that may traverse low-bandwidth or congested links. This can violate latency, jitter, or bandwidth SLAs for real-time or SLA-sensitive traffic flows until the primary path is restored.

Concept tested: Loop-Free Alternate IP Fast Reroute design tradeoffs

Source: https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/iproute_ospf/configuration/xe-16/iro-xe-16-book/iro-ip-fast-reroute.html

Topics

#Loop-Free Alternate#fast reroute#backup path#SLA

Community Discussion

No community discussion yet for this question.

Full 352-001 Practice