The correct answer is LISP and VXLAN, as these two protocols form the essential overlay foundation for SD-Access fabric segmentation. LISP provides the centralized control plane by separating endpoint identity (EID) from its location (RLOC), enabling policy-based forwarding and scalable mapping across the fabric, while VXLAN handles the data-plane encapsulation necessary to extend Layer 2 and Layer 3 segments over the IP underlay. On the ENCOR 350-401 exam, this pairing tests your understanding of how SD-Access decouples control and data planes—a common trap is confusing VXLAN as a control-plane protocol, when it is strictly a data-plane encapsulation method. Remember the mnemonic: LISP maps the who (identity) to the where (location), and VXLAN wraps the traffic to get it there.
350-401 SD-Access Architecture Practice Question
This 350-401 practice question tests your understanding of sd-access architecture. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. 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.
A network architect is designing an SD-Access fabric for a large enterprise campus. The design must support segmentation at Layer 2 and Layer 3 across the fabric, using a centralized control plane and policy enforcement. Which two protocols are essential for the SD-Access overlay to meet these requirements?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
LISP and VXLAN
LISP (Locator/ID Separation Protocol) provides the centralized control plane for endpoint identity-to-location mapping and policy-based forwarding, while VXLAN (Virtual Extensible LAN) supplies the data-plane encapsulation needed for Layer 2 and Layer 3 segmentation across the underlay. Together, they enable scalable overlay segmentation with a centralized policy enforcement point in SD-Access.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✓
LISP and VXLAN
Why this is correct
LISP provides the control plane and VXLAN provides the data plane encapsulation for the overlay.
Related concept
Read the scenario before looking for a memorised answer.
✗
MP-BGP and MPLS
Why it's wrong here
MP-BGP and MPLS are used in MPLS VPN designs, not the SD-Access overlay.
✗
OSPF and GRE
Why it's wrong here
OSPF is an underlay routing protocol and GRE is a generic tunnel; not the primary overlay protocols for SD-Access.
✗
IS-IS and NVGRE
Why it's wrong here
IS-IS can be used in the underlay, but NVGRE is not used in Cisco SD-Access.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that MPLS or EVPN is the required overlay for SD-Access, but the exam specifically expects LISP and VXLAN as the essential protocols for the fabric overlay.
Detailed technical explanation
How to think about this question
In SD-Access, LISP separates the endpoint identifier (EID) from its routing locator (RLOC), allowing the fabric border and control plane node to maintain a centralized mapping database. VXLAN encapsulates Ethernet frames with a VNI (VXLAN Network Identifier) to support up to 16 million segments, enabling both Layer 2 and Layer 3 overlay networks. A common real-world scenario is a campus with multiple virtual networks (VNs) where LISP handles host mobility and policy, while VXLAN ensures traffic isolation across the same physical underlay.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 350-401 question in full detail.
SD-Access Architecture — This question tests SD-Access Architecture — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: LISP and VXLAN — LISP (Locator/ID Separation Protocol) provides the centralized control plane for endpoint identity-to-location mapping and policy-based forwarding, while VXLAN (Virtual Extensible LAN) supplies the data-plane encapsulation needed for Layer 2 and Layer 3 segmentation across the underlay. Together, they enable scalable overlay segmentation with a centralized policy enforcement point in SD-Access.
What should I do if I get this 350-401 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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