- A
In echo mode, the remote router generates and sends the echo packets back to the local router.
Why wrong: Incorrect. The local router generates the echo packets; the remote router only reflects them back without generating new packets.
- B
Echo mode reduces the processing load on the remote router because it does not need to process BFD control packets.
Correct. The remote router simply loops back the echo packets at Layer 2, avoiding BFD control packet processing.
- C
BFD echo mode can be used for both single-hop and multihop BFD sessions.
Correct. Echo mode is supported for both single-hop and multihop BFD sessions, though it is more commonly used in single-hop scenarios.
- D
When echo mode is enabled, the BFD control packet interval must be set to a lower value than the echo interval.
Why wrong: Incorrect. There is no such requirement; the control packet interval and echo interval are independent and can be configured separately.
- E
Echo mode requires the bfd echo command under the BFD neighbor configuration.
Why wrong: Incorrect. Echo mode is enabled globally or per interface using the bfd echo command, not per neighbor.
Quick Answer
The correct answer is that BFD echo mode can be used for both single-hop and multihop BFD sessions. This is true because echo mode offloads processing from the remote router: the local router sends echo packets, and the remote router simply loops them back without inspecting or generating BFD control packets, drastically reducing CPU overhead on the far end. On the Cisco CCNP ENARSI 300-410 exam, this concept tests your understanding of how BFD minimizes control-plane load, and a common trap is assuming echo mode only works for directly connected single-hop neighbors—when in fact it is fully supported for multihop sessions as well. Remember that echo mode is enabled per interface or per neighbor, and the key benefit is that the remote router never has to process a BFD control packet for that session. Memory tip: think “Echo = Local sends, Remote reflects—no work for the reflector.”
300-410 Bidirectional Forwarding Detection (BFD) Practice Question
This 300-410 practice question tests your understanding of bidirectional forwarding detection (bfd). 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 TWO statements about BFD echo mode are true? (Choose TWO.)
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
Echo mode reduces the processing load on the remote router because it does not need to process BFD control packets.
BFD echo mode reduces control packet processing overhead by having the remote router loop back echo packets. The local router sends echo packets, and the remote router simply reflects them back without processing BFD control packets. This reduces CPU load on the remote router, but the local router still generates and processes the echo packets. BFD echo mode is supported for both single-hop and multihop sessions, and it can be enabled per interface or per neighbor.
Key principle: OSPF neighbour adjacency depends on matching area, hello/dead timers, network type, and authentication — IP reachability alone is not enough.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
In echo mode, the remote router generates and sends the echo packets back to the local router.
Why it's wrong here
Incorrect. The local router generates the echo packets; the remote router only reflects them back without generating new packets.
- ✓
Echo mode reduces the processing load on the remote router because it does not need to process BFD control packets.
Why this is correct
Correct. The remote router simply loops back the echo packets at Layer 2, avoiding BFD control packet processing.
Related concept
OSPF neighbours must agree on key parameters.
- ✓
BFD echo mode can be used for both single-hop and multihop BFD sessions.
Why this is correct
Correct. Echo mode is supported for both single-hop and multihop BFD sessions, though it is more commonly used in single-hop scenarios.
Related concept
OSPF neighbours must agree on key parameters.
- ✗
When echo mode is enabled, the BFD control packet interval must be set to a lower value than the echo interval.
Why it's wrong here
Incorrect. There is no such requirement; the control packet interval and echo interval are independent and can be configured separately.
- ✗
Echo mode requires the bfd echo command under the BFD neighbor configuration.
Why it's wrong here
Incorrect. Echo mode is enabled globally or per interface using the bfd echo command, not per neighbor.
Common exam traps
Common exam trap: OSPF can fail even when IP connectivity looks correct
OSPF neighbour formation depends on matching areas, timers, network type, authentication and passive-interface behaviour. Do not choose an answer only because the devices can ping.
Trap categories for this question
Command / output trap
Incorrect. Echo mode is enabled globally or per interface using the bfd echo command, not per neighbor.
Detailed technical explanation
How to think about this question
OSPF questions usually test the details that control adjacency and route selection. Read the neighbour state, area, router ID and interface configuration before deciding what is wrong.
KKey Concepts to Remember
- OSPF neighbours must agree on key parameters.
- Router ID selection can affect neighbour relationships and LSDB output.
- OSPF cost influences the preferred path.
- A route can appear in OSPF information but not become the installed route.
TExam Day Tips
- Check area mismatch first when OSPF adjacency fails.
- Review passive interfaces when a network is advertised but no neighbour forms.
- Use show ip ospf neighbor and show ip route clues carefully.
Key takeaway
OSPF neighbour adjacency depends on matching area, hello/dead timers, network type, and authentication — IP reachability alone is not enough.
Real-world example
How this comes up in practice
A network engineer at a university connects two campus buildings via a fibre link. Both routers run OSPF, but no adjacency forms — even though both routers can ping each other. The engineer finds one router is in area 0 and the other in area 1. OSPF adjacency requires matching area numbers, hello/dead timers, and network type. IP reachability alone is not enough.
What to study next
Got this wrong? Here's your next step.
Review OSPF neighbour requirements — matching area type, hello and dead timers, network type, stub flags, and authentication. Study show ip ospf neighbor states (INIT, 2-WAY, FULL). Then practise related 300-410 OSPF questions on adjacency and route selection.
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FAQ
Questions learners often ask
What does this 300-410 question test?
Bidirectional Forwarding Detection (BFD) — This question tests Bidirectional Forwarding Detection (BFD) — OSPF neighbours must agree on key parameters..
What is the correct answer to this question?
The correct answer is: Echo mode reduces the processing load on the remote router because it does not need to process BFD control packets. — BFD echo mode reduces control packet processing overhead by having the remote router loop back echo packets. The local router sends echo packets, and the remote router simply reflects them back without processing BFD control packets. This reduces CPU load on the remote router, but the local router still generates and processes the echo packets. BFD echo mode is supported for both single-hop and multihop sessions, and it can be enabled per interface or per neighbor.
What should I do if I get this 300-410 question wrong?
Review OSPF neighbour requirements — matching area type, hello and dead timers, network type, stub flags, and authentication. Study show ip ospf neighbor states (INIT, 2-WAY, FULL). Then practise related 300-410 OSPF questions on adjacency and route selection.
What is the key concept behind this question?
OSPF neighbours must agree on key parameters.
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 →
Same concept, more angles
2 more ways this is tested on 300-410
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. Which TWO statements about BFD echo mode are true? (Choose TWO.)
hard- ✓ A.Echo packets are generated by the sending router and forwarded back by the remote router.
- ✓ B.Echo mode reduces the processing load on the remote router's control plane.
- C.Echo mode requires a separate BFD session for each direction.
- D.Echo mode increases the number of BFD control packets sent between routers.
- E.Echo mode is enabled by default on all interfaces.
Why A: In BFD echo mode, the sending router generates echo packets that are looped back by the remote router, allowing detection of failures without involving the remote router's control plane. This reduces CPU load on the remote router. The other statements are false because echo mode does not require a separate session for each direction, and it does not increase the number of BFD control packets.
Variation 2. Which of the following statements about BFD echo mode is true?
medium- A.Echo mode increases the load on the remote router because it must process echo packets.
- B.Echo mode is disabled by default and must be explicitly enabled.
- C.Echo mode uses the same timer values as the BFD control packets.
- ✓ D.Echo mode allows the local router to detect failures without requiring the remote router to send BFD control packets.
Why D: BFD echo mode is an optional mode where the local router sends echo packets to the remote router, which loops them back. This reduces the processing load on the remote router because it does not need to generate BFD control packets. Echo mode is enabled by default on Cisco IOS-XE.
Last reviewed: Jun 18, 2026
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