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300-410 Practice Question: Which THREE symptoms indicate a BFD session…

Which THREE symptoms indicate a BFD session failure? (Choose THREE.)

Answer choices

Why each option matters

Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.

Correct answer & explanation

The BFD neighbor state shows 'Down'

A BFD session failure typically results in the neighbor state being 'Down', the routing protocol (like OSPF or EIGRP) neighbor going down due to BFD's fast detection, and BFD timers expiring. The other options are not direct symptoms of a BFD session failure.

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 BFD neighbor state shows 'Down'

    Why this is correct

    A 'Down' state directly indicates session failure.

  • The OSPF neighbor state changes from Full to Down

    Why this is correct

    BFD triggers routing protocol neighbor down when BFD session fails.

  • BFD timer expiry messages appear in logs

    Why this is correct

    Timer expiry indicates that BFD did not receive expected packets, leading to session failure.

  • The interface MTU is set to 1500

    Why it's wrong here

    MTU setting is unrelated to BFD session state.

  • The BFD discriminator value is zero

    Why it's wrong here

    Discriminator values are assigned during session setup; a zero value may indicate configuration issues but is not a standard symptom of session failure.

Visual reference

R1 R2 R3 R4 10 100 10 100 OSPF picks R1→R2→R4 (cost 20) over R1→R3→R4 (cost 200)

Quick reference

Routing Protocol Comparison

ProtocolMetricMax HopsAlgorithmType
RIP v2Hop count15Bellman-FordDistance vector
OSPFCost (bandwidth)UnlimitedDijkstra (SPF)Link state
EIGRPComposite metricUnlimitedDUALHybrid
IS-ISCostUnlimitedDijkstraLink state
BGPPolicy / attributesUnlimitedPath vectorPath vector

RIP's 15-hop limit makes it unsuitable for large networks. OSPF and EIGRP dominate modern enterprise deployments.

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JA

Written by Johnson Ajibi, MSc IT Security

Senior Network & Security Engineer · founder of Courseiva

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