Question 238 of 2,015

SD-WAN Architecture →mediumDrag & DropObjective-mapped

Quick Answer

The correct order begins with the vEdge sending a BFD hello packet, followed by the remote vEdge responding with a BFD echo, then both sides agreeing on BFD timer values, the session moving to the Up state, and finally the session being used for path liveliness detection. This sequence is rooted in the Bidirectional Forwarding Detection protocol’s design for sub-second failure detection: the initial hello establishes a unidirectional path, the echo confirms bidirectional reachability, timer negotiation ensures consistent failure thresholds, and the Up state indicates the session is operational for liveliness monitoring. On the ENCOR 350-401 exam, this drag-and-drop task tests your understanding of SD-WAN control plane operations, specifically how vEdge routers verify overlay tunnel health before forwarding data. A common trap is confusing the echo response with the hello, or placing timer negotiation after the Up state—remember that timers must be agreed upon before the session can go Up. Memory tip: “Hello, Echo, Timers, Up, Liveliness” (HETUL) helps recall the five-step flow in order.

350-401 SD-WAN Architecture Practice Question

This 350-401 practice question tests your understanding of sd-wan architecture. 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.

Drag and drop the steps of BFD session establishment for path liveliness into the correct order, from first to last.

Clue words in this question

Noticing these words before you look at the options changes how you read each choice.

Clue: "first"
Why it matters: Order matters here. You are being tested on which action comes before the others — not which action is generally useful.

Question 1mediumdrag order

Read the full NAT/PAT explanation →

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

✓

vEdge sends BFD hello on each TLOC

BFD session establishment starts with the vEdge sending a BFD hello packet, the remote vEdge responds with a BFD echo, then both agree on the BFD timer values, the session moves to the Up state, and finally the session is used for path liveliness detection.

Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.

Common exam traps

Common exam trap: NAT rules depend on direction and matching traffic

NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.

Detailed technical explanation

How to think about this question

NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.

KKey Concepts to Remember

Static NAT maps one inside address to one outside address.
PAT allows many inside hosts to share one public address using ports.
Inside local and inside global describe the private and translated addresses.
NAT ACLs identify traffic for translation, not always security filtering.

TExam Day Tips

Identify inside and outside interfaces first.
Check whether the scenario needs static NAT, dynamic NAT or PAT.
Do not confuse NAT matching ACLs with normal packet-filtering intent.

Key takeaway

NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.

Real-world example

How this comes up in practice

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

Got this wrong? Here's your next step.

Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related 350-401 NAT questions on configuration and troubleshooting.

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FAQ

Questions learners often ask

What does this 350-401 question test?

SD-WAN Architecture — This question tests SD-WAN Architecture — Static NAT maps one inside address to one outside address..

What is the correct answer to this question?

The correct answer is: vEdge sends BFD hello on each TLOC — BFD session establishment starts with the vEdge sending a BFD hello packet, the remote vEdge responds with a BFD echo, then both agree on the BFD timer values, the session moves to the Up state, and finally the session is used for path liveliness detection.

What should I do if I get this 350-401 question wrong?

Are there clue words in this question I should notice?

Yes — watch for: "first". Order matters here. You are being tested on which action comes before the others — not which action is generally useful.

What is the key concept behind this question?

Static NAT maps one inside address to one outside address.

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Same concept, more angles

1 more ways this is tested on 350-401

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. Drag and drop the steps of BFD session establishment for path liveliness into the correct order, from first to last.

medium

✓ A.Edge device detects new transport tunnel
✓ B.Edge sends BFD hello over the tunnel
✓ C.Remote edge responds with BFD echo
✓ D.Both edges negotiate BFD parameters
✓ E.BFD session reaches Up state and monitors path

Why A: BFD session establishment starts with the edge device detecting a new transport tunnel, then sending a BFD hello packet, the remote device responds with a BFD echo, the two devices negotiate parameters, and finally the session becomes Up and is used for liveliness monitoring.

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