Question 198 of 2,015

SD-Access Architecture →hardMultiple SelectObjective-mapped

Quick Answer

The correct answer is that VXLAN traffic between fabric nodes can be encrypted using MACsec, because VXLAN itself does not provide native encryption—it is a Layer 2 over Layer 3 encapsulation that relies on external security mechanisms like MACsec or IPsec for confidentiality. In Cisco SD-Access, VXLAN serves as the data plane encapsulation, using a 24-bit VNI to segment virtual networks, while the control plane is handled by LISP and the underlay is a routed Layer 3 network running IS-IS or OSPF. On the ENCOR 350-401 exam, this question tests your ability to distinguish VXLAN’s role from other fabric components; a common trap is assuming VXLAN provides encryption or that it operates over a Layer 2 underlay. Remember the memory tip: “VXLAN carries, LISP controls, MACsec secures”—this keeps the three planes of SD-Access distinct.

350-401 SD-Access Architecture Practice Question

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

Which three statements about VXLAN in Cisco SD-Access are true? (Choose three.)

Question 1hardmulti select

Study the full SD-Access breakdown →

A
VXLAN encapsulation uses a 24-bit VNI to identify the virtual network.
Correct because the VXLAN Network Identifier (VNI) is a 24-bit field that uniquely identifies a Layer 2 or Layer 3 virtual network within the fabric.
B
The underlay network for VXLAN must be a Layer 2 switched network.
Why wrong: Incorrect because the underlay is a Layer 3 routed network (e.g., IS-IS, OSPF) that provides IP connectivity between fabric nodes.
C
VXLAN encapsulation is performed by the fabric edge node when traffic enters the fabric.
Correct because the fabric edge encapsulates traffic from endpoints into VXLAN packets before sending them across the fabric.
D
VXLAN provides the control plane for endpoint discovery in SD-Access.
Why wrong: Incorrect because VXLAN is only a data plane encapsulation; the control plane is provided by LISP (Locator/ID Separation Protocol).
E
VXLAN traffic between fabric nodes can be encrypted using MACsec.
Correct because MACsec (IEEE 802.1AE) can be used to encrypt VXLAN traffic on the wire between fabric nodes for additional security.

Full breakdown with real-world context →

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

✓

VXLAN encapsulation uses a 24-bit VNI to identify the virtual network.

VXLAN is the data plane encapsulation used in SD-Access to carry traffic across the fabric. It uses a 24-bit VNI to identify the virtual network (VN). The underlay network is typically a Layer 3 routed network using IS-IS or OSPF, not a Layer 2 network. VXLAN encapsulation is performed by the fabric edge node when traffic enters the fabric. The control plane for SD-Access uses LISP, not VXLAN itself. VXLAN does not provide encryption natively; MACsec or other encryption methods are used separately.

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.

✓
VXLAN encapsulation uses a 24-bit VNI to identify the virtual network.
Why this is correct
Correct because the VXLAN Network Identifier (VNI) is a 24-bit field that uniquely identifies a Layer 2 or Layer 3 virtual network within the fabric.
Related concept
OSPF neighbours must agree on key parameters.
✗
The underlay network for VXLAN must be a Layer 2 switched network.
Why it's wrong here
Incorrect because the underlay is a Layer 3 routed network (e.g., IS-IS, OSPF) that provides IP connectivity between fabric nodes.
✓
VXLAN encapsulation is performed by the fabric edge node when traffic enters the fabric.
Why this is correct
Correct because the fabric edge encapsulates traffic from endpoints into VXLAN packets before sending them across the fabric.
Related concept
OSPF neighbours must agree on key parameters.
✗
VXLAN provides the control plane for endpoint discovery in SD-Access.
Why it's wrong here
Incorrect because VXLAN is only a data plane encapsulation; the control plane is provided by LISP (Locator/ID Separation Protocol).
✓
VXLAN traffic between fabric nodes can be encrypted using MACsec.
Why this is correct
Correct because MACsec (IEEE 802.1AE) can be used to encrypt VXLAN traffic on the wire between fabric nodes for additional security.
Related concept
OSPF neighbours must agree on key parameters.

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.

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 350-401 OSPF questions on adjacency and route selection.

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FAQ

Questions learners often ask

What does this 350-401 question test?

SD-Access Architecture — This question tests SD-Access Architecture — OSPF neighbours must agree on key parameters..

What is the correct answer to this question?

The correct answer is: VXLAN encapsulation uses a 24-bit VNI to identify the virtual network. — VXLAN is the data plane encapsulation used in SD-Access to carry traffic across the fabric. It uses a 24-bit VNI to identify the virtual network (VN). The underlay network is typically a Layer 3 routed network using IS-IS or OSPF, not a Layer 2 network. VXLAN encapsulation is performed by the fabric edge node when traffic enters the fabric. The control plane for SD-Access uses LISP, not VXLAN itself. VXLAN does not provide encryption natively; MACsec or other encryption methods are used separately.

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

What is the key concept behind this question?

OSPF neighbours must agree on key parameters.

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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. Which three statements about VXLAN encapsulation in Cisco SD-Access are true? (Choose three.)

hard

✓ A.VXLAN encapsulation uses a 24-bit VNI to identify the virtual network segment.
✓ B.The VXLAN header in SD-Access includes a Group Policy ID field to carry the SGT.
C.VXLAN encapsulation in SD-Access is an IP-in-IP tunneling mechanism.
✓ D.The outer IP destination address in the VXLAN packet is the IP address of the destination fabric node.
E.The VNI is mapped to a VLAN at the fabric edge to provide Layer 2 connectivity for endpoints.

Why A: VXLAN in SD-Access uses a 24-bit VNI for network segmentation, and the fabric encapsulation adds a VXLAN header plus an outer IP/UDP header. The fabric uses VXLAN with Group Policy Option (GPO) to carry SGT information in the header. VXLAN is a MAC-in-UDP encapsulation, not IP-in-IP. The VNI is used to identify the virtual network (VN) and is mapped to a VLAN at the edge. The outer source IP is typically the loopback of the fabric node, not the end-user IP.

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