As the adoption of software-defined wide-area networking (SD-WAN) continues to grow, organizations are increasingly seeking professionals with expertise in this technology. During the interview process, candidates can expect to be asked a variety of questions related to SD-WAN troubleshooting and design. These questions are intended to assess the candidate's knowledge, problem-solving skills, and ability to apply their understanding of SD-WAN in practical scenarios.

In this blog post, we'll explore some common SD-WAN troubleshooting and design questions that often come up in interviews, along with insights on how to approach and answer them effectively.

Common SD-WAN Troubleshooting Questions

1. Describe the process of troubleshooting an SD-WAN network connection issue.

When troubleshooting an SD-WAN network connection issue, the process typically involves the following steps:

1. Gather information: Collect relevant details about the problem, such as the affected sites, the symptoms, any error messages, and the timeline of when the issue started.
2. Analyze the SD-WAN dashboard: Review the SD-WAN dashboard to identify any alerts, performance metrics, or configuration changes that may be contributing to the problem.
3. Check the SD-WAN device status: Verify the status of the SD-WAN devices (e.g., routers, gateways) at the affected sites, including their connectivity, software versions, and any error logs.
4. Examine the network topology: Understand the overall SD-WAN network topology, including the various transport links (e.g., MPLS, broadband, LTE) and how they are configured.
5. Perform troubleshooting tests: Conduct connectivity tests, such as pinging, traceroute, or using built-in SD-WAN tools, to identify the specific point of failure.
6. Isolate the problem: Determine whether the issue is related to the SD-WAN overlay, the underlying transport links, or a combination of both.
7. Implement a solution: Based on the findings, take the necessary actions to resolve the problem, such as reconfiguring the SD-WAN settings, troubleshooting the transport links, or escalating to the appropriate vendor or service provider.
8. Verify the resolution: Confirm that the problem has been resolved and monitor the network for any recurring issues.

By following this structured approach, you can effectively troubleshoot and resolve SD-WAN network connection problems.

2. How would you troubleshoot a scenario where an SD-WAN site is unable to establish a secure overlay tunnel with the central SD-WAN controller?

To troubleshoot a scenario where an SD-WAN site is unable to establish a secure overlay tunnel with the central SD-WAN controller, you can follow these steps:

1. Verify the SD-WAN device configuration: Ensure that the SD-WAN device at the affected site is properly configured with the correct IP address, credentials, and any necessary certificates or keys for secure communication with the central controller.
2. Check the network connectivity: Verify the network connectivity between the SD-WAN device and the central controller. Perform tests like ping, traceroute, or use built-in SD-WAN tools to identify any network issues or firewalls that may be blocking the communication.
3. Examine the SD-WAN controller logs: Review the logs on the central SD-WAN controller to identify any error messages or clues that may indicate the reason for the failed tunnel establishment.
4. Inspect the SD-WAN device logs: Check the logs on the SD-WAN device at the affected site for any relevant error messages or information that could help pinpoint the problem.
5. Validate the security configurations: Ensure that the security configurations, such as firewall rules, encryption settings, and authentication mechanisms, are properly configured on both the SD-WAN device and the central controller.
6. Verify the routing and policy configurations: Ensure that the routing and policy configurations on the SD-WAN device and the central controller are aligned and do not have any conflicting rules that could prevent the secure tunnel from being established.
7. Perform a factory reset or firmware update: If the issue persists, consider performing a factory reset on the SD-WAN device or updating the firmware to the latest version, as this may resolve any underlying software or configuration problems.
8. Escalate to the vendor or service provider: If you are unable to resolve the issue, escalate the problem to the SD-WAN vendor or service provider for further assistance and investigation.

By systematically working through these steps, you can effectively troubleshoot and resolve the issue with the secure overlay tunnel establishment between the SD-WAN site and the central controller.

3. How would you troubleshoot a scenario where an SD-WAN site is experiencing poor application performance?

When troubleshooting poor application performance in an SD-WAN environment, you can follow these steps:

1. Gather application performance data: Collect relevant performance metrics, such as application response times, network latency, packet loss, and jitter, from the SD-WAN dashboard or monitoring tools.
2. Analyze the SD-WAN traffic patterns: Review the SD-WAN traffic patterns to identify any anomalies, such as sudden spikes in bandwidth usage, changes in application mix, or imbalanced traffic distribution across the available transport links.
3. Examine the SD-WAN policies and routing configurations: Verify that the SD-WAN policies and routing configurations are properly configured to prioritize and steer the application traffic to the appropriate transport links based on the application requirements and performance SLAs.
4. Check the transport link quality: Evaluate the quality of the underlying transport links (e.g., MPLS, broadband, LTE) by analyzing metrics like bandwidth, latency, and packet loss. Identify any potential issues with the transport links that could be impacting the application performance.
5. Verify the application-level configurations: Ensure that the application-level configurations, such as load balancing, caching, and optimization settings, are properly configured to leverage the capabilities of the SD-WAN network.
6. Perform application-specific tests: Conduct targeted tests for the specific application experiencing performance issues, such as running synthetic transactions or using application-level monitoring tools to identify the root cause of the problem.
7. Analyze the SD-WAN device and controller logs: Review the logs on the SD-WAN devices and the central controller for any error messages, resource utilization spikes, or other indicators that could be contributing to the poor application performance.
8. Implement remediation actions: Based on the findings, take the necessary actions to resolve the performance issue, such as adjusting the SD-WAN policies, optimizing the transport link configurations, or updating the application-level settings.
9. Verify the resolution: Confirm that the application performance has improved after implementing the remediation actions and continue to monitor the network for any recurring issues.

By following this systematic approach, you can effectively troubleshoot and resolve poor application performance in an SD-WAN environment.

Common SD-WAN Design Questions

4. How would you design an SD-WAN solution for a multi-site organization with the following requirements:

• Ensure high availability and redundancy for mission-critical applications
• Optimize network performance and application delivery
• Provide secure remote access for mobile users
• Reduce the overall WAN costs

When designing an SD-WAN solution for a multi-site organization with the given requirements, you can consider the following key elements:

1. Network Topology and Transport Links:

   • Implement a hub-and-spoke or a full-mesh SD-WAN topology, depending on the organization's needs and the geographical distribution of the sites.
   • Leverage a combination of transport links, such as MPLS, broadband internet, and LTE, to provide redundancy and ensure high availability.
   • Configure the SD-WAN devices to automatically detect and failover to the best available transport link based on performance metrics and application requirements.

2. High Availability and Redundancy:

   • Deploy SD-WAN devices in a high-availability (HA) configuration at each site, with primary and backup devices for redundancy.
   • Implement dynamic path selection and load balancing across the available transport links to ensure continuous connectivity and optimal performance for mission-critical applications.
   • Configure the SD-WAN solution to automatically detect and reroute traffic in the event of a transport link or device failure, minimizing downtime.

3. Application Optimization and Performance:

   • Implement advanced SD-WAN features, such as application-aware routing, dynamic path selection, and quality of service (QoS) policies, to prioritize and optimize the delivery of mission-critical applications.
   • Leverage SD-WAN's ability to steer traffic across the best-performing transport links based on real-time network conditions and application requirements.
   • Explore the use of SD-WAN-integrated optimization techniques, such as WAN optimization, caching, and compression, to enhance application performance.

4. Secure Remote Access:

   • Integrate the SD-WAN solution with a secure remote access solution, such as a virtual private network (VPN) or a zero-trust network access (ZTNA) platform.
   • Ensure that remote users can securely connect to the SD-WAN network and access the necessary resources, regardless of their location or device.
   • Implement robust security measures, such as multi-factor authentication, encryption, and granular access controls, to protect the remote access infrastructure.

5. Cost Optimization:

   • Leverage the cost-effective broadband internet links as the primary transport, reserving the more expensive MPLS links for mission-critical traffic or as backup connections.
   • Explore SD-WAN's ability to dynamically steer traffic across the available transport links based on cost, performance, and application requirements to optimize the overall WAN costs.
   • Identify opportunities to consolidate or replace legacy WAN technologies (e.g., MPLS) with more cost-effective SD-WAN-enabled solutions.

By incorporating these key design elements, you can create an SD-WAN solution that meets the organization's requirements for high availability, optimal performance, secure remote access, and cost-effectiveness.

5. How would you design an SD-WAN solution to enable secure branch-to-cloud connectivity for a distributed organization?

When designing an SD-WAN solution to enable secure branch-to-cloud connectivity for a distributed organization, you can consider the following key elements:

1. Cloud Connectivity Architecture:

   • Implement a hub-and-spoke or a full-mesh SD-WAN topology, with the central SD-WAN controller and cloud gateways serving as the hub.
   • Configure the branch SD-WAN devices to establish secure overlay tunnels directly to the cloud gateways, bypassing the traditional data center.
   • Ensure that the cloud gateways are strategically located to provide optimal connectivity and low latency to the cloud services and applications.

2. Secure Connectivity:

   • Leverage the built-in security features of the SD-WAN solution, such as end-to-end encryption, to ensure secure communication between the branch sites and the cloud.
   • Integrate the SD-WAN solution with a cloud-based security platform, such as a secure web gateway (SWG) or a cloud access security broker (CASB), to provide comprehensive security for cloud-bound traffic.
   • Implement robust access controls, user authentication, and authorization mechanisms to ensure that only authorized users and devices can access the cloud resources.

3. Application Optimization:

   • Configure the SD-WAN solution to prioritize and optimize the delivery of cloud-based applications, leveraging features like application-aware routing, dynamic path selection, and QoS policies.
   • Explore the use of SD-WAN-integrated optimization techniques, such as WAN optimization and caching, to enhance the performance of cloud-based applications.
   • Monitor the performance of cloud-bound traffic and make adjustments to the SD-WAN policies and configurations as needed to maintain optimal application delivery.

4. Visibility and Monitoring:

   • Implement a centralized monitoring and analytics platform that can provide visibility into the end-to-end performance and security of the branch-to-cloud connectivity.
   • Leverage the SD-WAN solution's built-in monitoring and reporting capabilities to track key metrics, such as bandwidth utilization, latency, packet loss, and application performance.
   • Integrate the SD-WAN monitoring with the organization's existing network management and security tools to ensure a comprehensive view of the hybrid network.

5. Scalability and Flexibility:

   • Design the SD-WAN solution to be scalable, allowing for the easy onboarding of new branch sites and the seamless integration of additional cloud services and applications.
   • Ensure that the SD-WAN solution is flexible enough to accommodate changes in the organization's cloud strategy, such as the addition of new cloud providers or the migration of applications to different cloud platforms.

By incorporating these key design elements, you can create an SD-WAN solution that enables secure, optimized, and scalable branch-to-cloud connectivity for a distributed organization.

Conclusion

Navigating the world of SD-WAN troubleshooting and design can be a complex and challenging task, but by understanding the common questions and approaches, you can better prepare for successful interviews and demonstrate your expertise in this rapidly evolving technology.

Remember, the key to answering these questions effectively is to have a deep understanding of SD-WAN concepts, a structured problem-solving approach, and the ability to apply your knowledge to real-world scenarios. By showcasing your SD-WAN expertise, you can position yourself as a valuable asset to any organization looking to deploy and maintain a robust and efficient SD-WAN infrastructure.