Top 25 SD-WAN Interview Questions and Answers (2025)

Introduction

SD-WAN is the most widely deployed solution within the industry and its increasing demand can only be fulfilled by Network Engineers with SD-WAN designing and deployment skills.

By any chance, if you being a Network Engineer, are going to appear for such a job role then here are the SD-WAN interview questions and answers that should be at your fingertips. These SD-WAN interview questions are curated by the combined efforts of some of the leading recruiters and our SD-WAN training leaders.

About SD-WAN

SD-WAN is a software-defined networking technology for optimizing and securing Wide Area Networks. It is based on the SDN Technology. SD-WAN simplifies network management and improves application performance. It is also used to decrease cost of WANs by optimizing the best route for data traffic.

Let’s move on to see some basic SD-WAN Interview Questions and Answers.

Basic SD-WAN Interview Questions and Answers

Here are the top most asked SD-WAN interview questions that you should be prepared to face in any SD-WAN interview.

Q1. What is the SD-WAN solution?

The traditional Wide Area Networks (WAN) were created using MPLS to connect the large proportions of office traffic that is carried within an intranet’s boundary of the enterprise. However, New Cloud Applications such as Microsoft Office 365, Salesforce and Public Cloud Services such as Amazon Web Services and Azure are transforming traffic patterns.

Today, the majority of Enterprise Traffic flows to Public Clouds and the Internet. This has created new requirements for all-in-all security, application performance, Cloud connectivity, WAN Management and operations. SD-WAN provides a brand-new method to manage and operate WAN Infrastructure. It offers a cloud-based solution that offers an efficient, secure and rich service architecture. Salesforce integration services can also make this approach better by facilitating smooth and safe data movement between your on-premise network and Salesforce instances, thereby improving performance and user experience.

Q2. What are the key benefits offered by SD-WAN?

The key benefits offered by SD-WAN are:

• More User-Friendly Experience – Develop applications in just a few minutes across all platforms and enjoy an unmatched user experience.
• Greater Agility – SD-WAN simplifies the deployment and operation of your WAN and improves performance by using lesser bandwidth. Also, it offers the freedom to set up your WAN using any kind of connection like MPLS, Internet, or 4G LTE.
• Secure Connectivity – SD-WAN securely connects users to apps in a matter of minutes and safeguards your WAN Edge data to the cloud.

Q3. Which problem can a SD-WAN overcome?

Here are a few issues that SD-WAN Solutions overcome:

• Create a transport-independent WAN for high diversity and low cost
• Be in compliance with Service Level Agreements (SLAs) for critical business and real-time applications
• Create End-to-End Segmentation in order to safeguard the most critical computing resources of an enterprise
• Optimal User Experience for SaaS and IaaS applications.

Q4. What are vSmart controllers?

vSmart Controllers form the central part of the solution which establishes policies and connections between branches of the SD-WAN. The central policy engine of Cisco vSmart Controllers offers policies that can be used to alter routing information, access control, segmentation as well as extranets and chaining services.

Q5. What are vBond orchetrators?

The vBond orchestrator helps with the initial set-up process by ensuring authentication and authorization for all elements in the network. Cisco vBond Orchestrator additionally gives information about how each component communicates with other elements. Cisco vBond orchestrator plays an essential role in the facilitation of Cisco SD-WAN devices which sit behind the Network Address Translation (NAT) to connect to the network.

Q6. What is Cisco vManage?

Cisco vManage manages the entire solution. Cisco’s GUI is centralized management and provisioning platform that is available for days 0, 1 and day plus for the whole Cisco SD-WAN system. You can log in on the Cisco vManage dashboard to manage and centrally control the WAN. Cisco vManage gives you the capability to manage every aspect of the WAN from setting up, monitoring, and updating routers, to monitoring and troubleshooting applications on the WAN.

Q7. Is the Cisco SD-WAN solution secure?

SD-WAN connects security and networking together unlike any other technology. SDWAN offer extremely efficient and scalable security that’s simple to deploy, manage, and maintain, helping companies to take advantage of the latest cloud technology with confidence.

SD-WAN is built on a zero-trust concept and the multilayer security secures every data stream to ensure security starting from the WAN Edge to Cloud. The entire set of SD-WAN components are able to mutually authenticate one another and all edge devices have to be authorized prior to be allowed access to the network. Each and every packet across the control plane, data plane and management plane that flows through the network is secured with Secure Socket Layer (SSL) and IP Security (IPsec) technologies. The SD-WAN Solution offers distinct capabilities that are integrated to create an extensive IPsec network that spans many branches.

Q8. Does SD-WAN solution support network segmentation and what are the benefits?

Yes, it is true that the SD-WAN solution supports the segmentation of the network. Segmentation allows for secure logical isolation in the SD-WAN network in which each segment is identified as a distinct VPN, and is controlled centrally by access control policies.

 Some of the Benefits of Segmentation:

1. Increased security – Protect your network from external threats and establish a secure segregation across multiple application segments.
2. Acquisitions can be integrated onto the parent network, but remain separated. Policies determine what applications an acquired company is able to access.
3. Guest Wi-Fi is maintained on a separate low-priority section and then transferred to the Internet at the nearest exit points.
4. Business partners may be defined as a distinct segment or as a group networking segment for business partners.
5. Polices manage access of business partners to data center applications.

Q9. How did viptela SD-WAN help in architectural transformation?

• Transport Independence: Viptela SD-WAN separates the service away from the physical networks and creates an overlay over any connectivity options an organization has. This allows for transport independence and is not tied to any particular type of service.
• Security At Routing Scale: Viptela SD-WAN offers security by means of encryption and devices authentication. The founders tapped their experience in routing protocols to create an encryption solution that offers security from any angle. The Viptela router is able to connect any entity and then automatically redirect the traffic among them like they were an identical VPN connection.
• Network-Wide Segmentation: Since Viptela technology allows overlay, businesses can segment the network in a way that is end-to-end. It is possible to segment the network on an end-to-end basis. Viptela SD-WAN lets an organization create multiple logical topologies in any way they like and also, each of these distinct segments of the network may have different encryption strategies.
• Enforce Policy and Business Logic Centrally: Each network location is responsible for the policies of that specific area; however, each location is affected by the centralized controller. If required an organization can have multiple controllers in order to meet the needs for resilience.
• Insert Layer 4-7 Services on Demand: Viptela SD-WAN lets layer 4-7 services on networks be promoted by allowing companies to create any service from a third party on that network to connect with the Viptela overlay. After that, anyone who wishes to make use of these services creates the policy centrally to direct traffic to a specific location.

Q10. What benefits do SD-WAN and routing subscription offer?

 The latest licensing deals bring customers these advantages:

1. Newest Innovations with Simple Subscription Tiers: It is easy to purchase and simple to use via Cisco DNA Essentials, Advantage, or Premier Software Suite.
2. Management Flexibility: Choice of Cloud or On-premises Management.
3. Availability Across the Routing Stack:

• Across the Cisco ASR 1000 Aggregation Series Service Routers,
• Cisco 1000 Integration Series Routers (ISR 1000) and
• Cisco 4000 Integration Series Routers (ISR 4000),
• Cisco Cloud Services Routers 1000 Series (CSR 1000V),
• Cisco 5000 Series Enterprise Compute System (ENCS 5000), and
• Cisco vEdge Routers

4. Software License Portability: Between different generations of hardware as well as among product family (for example, vEdge and ISR and across ISR platforms) Ability to renew and expand what you need whenever you need to.

These are some of the most asked basic SD-WAN Interview Questions and Answers.

Advanced SD-WAN Interview Questions and Answers

Here are the top most asked advanced level questions and answers –

Q11. Why should one opt for SDN?

There are multiple advantages of choosing SDN over traditional WAN such as:

• Better Application Experience
  • Predictable SLA on all vital enterprise applications
  • App-aware policies that have real-time enforcement of network issues
  • Multiple hybrid active-active links for every scenario
• Best in Class Integrated Security
  • Zero-trust foundation that includes encryption and authentication
  • Segmentation is used to protect and isolate important assets using the cloud, guest wireless, partner networks, and more
  • Enterprise firewall, AMP, IPS, DNS-layer enforcement, URL filtering, A/V and SSL decryption proxy are all integrated into SD-WAN
• Cloud Optimization
  • It is easy to connect your WAN to multiple cloud providers
  • Real-time optimization in Office365, Salesforce as well as other important SaaS applications.
  • Improved workflows designed for AWS and Azure

Q12. What are the elements of SD-WAN?

Here are the Components of SD-WAN:

• vSmart Controller – Central control of routing, policies security, segmentation and device authentication.
• vManage Controller – A central dashboard for management and configuration.
• vEdge Routers – Fully-featured IP routers that perform standard functions like BGP, OSPF, ACLs, QoS, and a variety of routing policies, in addition to overlay communication.
• vBond Orchestrator – They are responsible for the Initial authentication and authorization of all elements into the network; It also provides information on how each of the components connects to other components.

Q13. What is site-id?

A site is a specific physical area in the Viptela Overlay Network, for example, a branch office or data center or even a campus. The site is identified with a Unicode number, known as the Site-ID. Every Viptela device that is located at a specific site is identified using the same site ID.

In a data center each of the vSmart controllers and vEdge routers are set up using the same site ID. Local sites or branch offices generally have one vEdge router. If another one is in place to ensure redundancy, both routers are set up using the same site ID.

Q14. What is a Virtual Private Network (VPN)?

In the SD-WAN overlay, Virtual Private Networks (VPNs) provide segmentation, just like Virtual Routing and Forwarding instances (VRFs) which many people are familiar with.

Each VPN is distinct from the others and has its own forwarding table. A sub-interface or interface is configured specifically under one VPN and can’t be an element of multiple VPNs. Labels are employed to identify the VPN in OMP route attributes as well as in the packet encapsulation process, which determines which VPN a particular packet is part of.

The VPN numbers are a 4-byte integer that has values ranging from 0 to 65530. The two VPNs that are by default in the vEdge controllers and devices are VPN 0 and VPN 512.

• VPN 0:

This is the transport VPN. It has interfaces to connect to WAN transports. Secure DTLS/TLS connections to vSmart between vSmart or vBond controllers are established through this VPN.

Moreover, the static or default or a dynamic routing protocol needs to be set up within this VPN for it to obtain proper next-hop information, so that it is possible to establish the control plane and IPSec tunnels could connect to distant sites.

• VPN 512: 

It is the management VPN. It is responsible for carrying the out-of-band management traffic to and from the Cisco SD-WAN devices. This VPN is not carried across the overlay network.

Q15. What are the specifications to be met for ZTP?

In the case of the hardware-based vEdge appliance, only certain ports are configured by default to be a DHCP client interface and then can be used for ZTP. The following table lists the ports that need to be connected to the network in order for ZTP to function.

1. The Gateway Router for the vEdge router within the network should be reachable to public DNS servers and should be capable of reaching ztp.viptela.com.
2. In vManage, it is necessary to have an appropriate device configuration template for the vEdge router connected with the vEdge device.
3. The system IP address as well as the site ID must be part of this device template in order for ZTP to function. The ZTP process is not successful without this.

Q16. What are the common SD-WAN challenges?

Some of the common challenges associated with SD-WAN:

• Integration with existing network infrastructure
• Managing Security
• Ensuring consistent performance across different WANs
• Complexity of network environments

Q17. What are the key metrics to monitor in an SD-WAN environment?

Some metrics that need to be monitored in an SD-WAN are:

• Network Latency
• Application performance
• Device health
• Bandwidth utilization
• Packet Loss
• Jitter

Q18. What is TLOC in SD-WAN?

TLOC in SD-WAN stands for Transport Locator. It is a crucial concept in Cisco SD-WAN as it represents an attachment point where a Cisco WAN Edge device connects to a WAN transport. It is used for:

• Tunnel Establishment – It is used to exchange information between SD-WAN edge devices to create overlay tunnels.
• Path Selection – TLOC evaluate various factors such as network condition, application requirement, and business policies to determine the best path for traffic.
• Load Balancing – TLOC are also used to distribute traffic across various WANs to improve performance.

TLOC consists of 3 components, which are – System IP Address, color, and Encapsulation.

Q19. How does SD-WAN handle network traffic prioritization?

SD-WAN uses a combination of features and configurations to prioritize network traffic. It ensures that critical applications get preferred treatment. The key mechanisms used to ensure network traffic prioritization are:

• Application-Aware Routing (AAR) – It identifies applications and assign them to specific network traffic classes. Then, it directs traffic based on application requirement and network condition.
• Quality of Service (QoS) – It priorities network traffic following various policies.
• Policy Based Routing (PBR) – It can be used to prioritize specific traffic flows.
• Load Balancing – Load Balancing is used to distribute traffic across various WANs.

This ensures critical applications receive higher priority and optimal performance by assigning traffic classes, marking packets, and intelligently distributing traffic across available WAN links.

Q20. Explain the concept of application SLA in SD-WAN.

Application SLA (Service Level Agreement) in SD-WAN defines the performance expectations for specific applications. It outlines the acceptable levels of latency, jitter, and packet loss for these applications.

Key elements of an Application SLA are –

• Application Identification
• Performance Metrics
• Monitoring and Enforcement

Some of the benefits of using Application SLA are:

• Improved User experience
• Enhanced network visibility
• Fast issue resolution

By establishing and managing application SLAs, organizations can optimize their SD-WAN network for delivering consistent and reliable application performance.

Scenario-Based SD-WAN Interview Questions and Answers

Here are some of the most-asked scenario-based SD-WAN Interview Questions and answers:

Q21. How would you troubleshoot a situation where a branch office is experiencing poor SD-WAN application performance?

The first step to troubleshooting this situation is checking the application performance metrics on the SD-WAN dashboard. Here, we must look for latency, jitter, or packet loss issues with the specific link used by the branch.

Next, verify the SLA (Service Level Agreement) policies applied to that application and ensure the traffic is routed through the right path. If we find a high-latency or congested link is being used, then we have to adjust the policy to prioritize a better link.

Finally, we can check for bandwidth utilization and QoS settings to make sure that they align with business-critical requirements. We can easily troubleshoot situations where a branch office is experiencing poor SD-WAN application performance using these steps.

Q22. A new branch is added to the SD-WAN network. How would you onboard it quickly?

To onboard a new branch in the SD-WAN network, we first deploy the SD-WAN edge device at the new branch and make sure that it is pre-configured or the zero-touch provisioning (ZTP) is enabled.

Next, we have to connect the new edge device to the internet to establish its connectivity with the SD-WAN Central controller. Once it is connected, we need to assign policies and templates specific to the branch’s requirements through the controller.

Finally, we check end-to-end connectivity and make sure that the applications are prioritized according to business needs.

Q23. How would you handle a scenario where SD-WAN fails over to a backup link but doesn’t revert to the primary link when restored?

For such a situation, we first check the failover and failback settings in the SD-WAN policy and make sure that the failback option is enabled.

Next, we must validate the SLA monitoring configuration for the primary link to make sure that it can detect when the link is restored. After these steps, the issue must be resolved.

However, if the issue persists, inspect whether the link health check thresholds are too strict or incorrectly configured, which might prevent automatic failback.

Q24. How would you design an SD-WAN solution for a business that uses hybrid cloud environments?

To design such a solution, we must first identify the key applications hosted in the hybrid cloud environment and map out their connectivity requirements. Use SD-WAN to establish direct connectivity between branch offices and public cloud providers through secure and optimized links.

Now, we will configure MPLS or private links for on-premises resources as required. Now, we will implement application-aware routing policies to prioritize critical workloads and ensure redundancy using failover links. At last, we will use SD-WAN security features like end-to-end encryption and firewalls for data protection.

Q25. What steps would you take if an SD-WAN edge device at a branch loses connection to the central controller?

We will start by making sure that the branch’s internet connection is active. After that, we will verify the connectivity between the edge device and the central controller using troubleshooting tools like ping or traceroute. We will check if the device’s configuration matches the controller’s requirements. If everything goes smoothly, the issues will be resolved.

However, if the issue persists, restart the edge device and re-establish communication. If zero-touch provisioning is enabled, it should automatically reconnect to the controller once the issue is resolved.

These are the top 25 SD-WAN Interview Questions and Answers. You can download the PDF for more interview questions on SD-WAN.

SD-WAN Interview Questions and Answers PDF

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Conclusion

We have covered all the most asked SD-WAN Interview questions and answers. Remember this is just a starting point, the depth of your knowledge will be the key to secure your dream SD-WAN job role. Practice delivering these answers confidently and prepare to discuss your past SD-WAN Experience. A few more additional tips to top your next SD-WAN interview –

• Stay updated with latest SD-WAN trends and technologies.
• Highlight your past experience with SD-WAN.
• Be confident and practice your labs again.

All the best for your Interview.