hardMultiple Choice
300-410 Practice Question: Runs the following command on Router R1: R1# show…
A network engineer runs the following command on Router R1:
R1# show bfd neighbors detail
IPv4 Sessions NeighborAddr LD/RD Int State Holdown(mult) Intf
10.1.1.2 1/3 Gi0/0 Down 0(0) Gi0/0
Session state is DOWN OurAddr: 10.1.1.1 Handle: 1 Local Diag: 1, Demand mode: 0, Poll bit: 0 MinTxInt: 1000000, MinRxInt: 1000000, Multiplier: 3 Received MinRxInt: 1000000, Received Multiplier: 3 Holddown (hits): 0(0) Rx Count: 0, Tx Count: 50
Based on this output, what is the most likely cause of the BFD session being down?
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 session is down because the neighbor is not responding to BFD packets, likely due to a network connectivity issue or neighbor misconfiguration.
The Local Diag field shows 1, which indicates 'Control Detection Time Expired'. This means the local router did not receive BFD control packets from the neighbor within the expected time. The Rx Count is 0, confirming no packets were received. Tx Count is 50, so the local router is sending packets but not receiving any.
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 neighbor router is not configured for BFD.
Why it's wrong here
Tx Count of 50 shows R1 is transmitting BFD control packets, so the neighbour is receiving them; the zero Rx Count means nothing arrives back, indicating a return-path or remote-side issue rather than absent configuration. It is tempting because an unconfigured neighbour produces a down session, but that would show zero transmitted packets.
- ✗
The BFD session is down because the local router is not sending BFD packets.
Why it's wrong here
The output contradicts this: Tx Count is 50, proving the local router is actively sending BFD control packets, while Rx Count is 0. It is tempting because a down session with no received packets suggests one side is silent, yet the counters localise the silence to the remote direction, not the local transmit path.
- ✓
The BFD session is down because the neighbor is not responding to BFD packets, likely due to a network connectivity issue or neighbor misconfiguration.
Why this is correct
The session shows Tx Count 50 with Rx Count 0, meaning R1 transmits control packets but receives none from 10.1.1.2. Local Diag 1 indicates no diagnostic fault locally, so the failure lies beyond R1 — a connectivity break or misconfigured neighbour prevents replies, satisfying the stem's evidence of one-way BFD traffic.
- ✗
The BFD session is down because the multiplier is set too low.
Why it's wrong here
The multiplier of 3 matches the value received from the neighbour, and detection timers only matter once packets flow; with Rx Count at 0, no echo or control packet ever arrives to time out. It is tempting because a low multiplier causes flapping, but that would show non-zero received counts.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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