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Chapter 35 — SD-WAN

A complete networking lesson based on the course chapter menu.

20 topicsPractical examplesTroubleshooting checksReview Q&A
Estimated reading time0% read

Chapter 35: SD-WAN

This chapter follows the topics shown in the Networking chapter menu. Work through each section in order, then use the review questions to check recall and troubleshooting reasoning.

35.1 SD-WAN Overview

SD-WAN uses centralized policy and an overlay to steer application traffic across multiple WAN transports according to availability, latency, loss, jitter, and business intent.

Example: place SD-WAN Overview in a small office network containing clients, switches, a router, wireless access, DNS/DHCP services, and an internet connection. Identify which device or layer owns the function and what evidence you would inspect to verify it.

What to check

  • Identify which OSI/TCP-IP layer and device type are primarily responsible.
  • Check configuration, interface or service state, counters, logs, and a simple end-to-end test.
  • Verify both normal operation and one realistic failure case so you understand what changes when the feature breaks.
Practice: Practice: explain SD-WAN Overview without reading the definition. Then draw or describe one network where it is used, name one failure symptom, and list the first two checks you would perform.

35.2 WAN Underlay

WAN Underlay is one of the core topics in SD-WAN. Understand what the term represents, where it operates in the network, what information it uses, and what observable behavior confirms that it is working correctly.

Example: place WAN Underlay in a small office network containing clients, switches, a router, wireless access, DNS/DHCP services, and an internet connection. Identify which device or layer owns the function and what evidence you would inspect to verify it.

What to check

  • Identify which OSI/TCP-IP layer and device type are primarily responsible.
  • Check configuration, interface or service state, counters, logs, and a simple end-to-end test.
  • Verify both normal operation and one realistic failure case so you understand what changes when the feature breaks.
Practice: Practice: explain WAN Underlay without reading the definition. Then draw or describe one network where it is used, name one failure symptom, and list the first two checks you would perform.

35.3 WAN Overlay

WAN Overlay is one of the core topics in SD-WAN. Understand what the term represents, where it operates in the network, what information it uses, and what observable behavior confirms that it is working correctly.

Example: place WAN Overlay in a small office network containing clients, switches, a router, wireless access, DNS/DHCP services, and an internet connection. Identify which device or layer owns the function and what evidence you would inspect to verify it.

What to check

  • Identify which OSI/TCP-IP layer and device type are primarily responsible.
  • Check configuration, interface or service state, counters, logs, and a simple end-to-end test.
  • Verify both normal operation and one realistic failure case so you understand what changes when the feature breaks.
Practice: Practice: explain WAN Overlay without reading the definition. Then draw or describe one network where it is used, name one failure symptom, and list the first two checks you would perform.

35.4 Centralized Policy

Centralized Policy is one of the core topics in SD-WAN. Understand what the term represents, where it operates in the network, what information it uses, and what observable behavior confirms that it is working correctly.

Example: place Centralized Policy in a small office network containing clients, switches, a router, wireless access, DNS/DHCP services, and an internet connection. Identify which device or layer owns the function and what evidence you would inspect to verify it.

What to check

  • Identify which OSI/TCP-IP layer and device type are primarily responsible.
  • Check configuration, interface or service state, counters, logs, and a simple end-to-end test.
  • Verify both normal operation and one realistic failure case so you understand what changes when the feature breaks.
Practice: Practice: explain Centralized Policy without reading the definition. Then draw or describe one network where it is used, name one failure symptom, and list the first two checks you would perform.

35.5 Multiple WAN Circuits

Multiple WAN Circuits is one of the core topics in SD-WAN. Understand what the term represents, where it operates in the network, what information it uses, and what observable behavior confirms that it is working correctly.

Example: place Multiple WAN Circuits in a small office network containing clients, switches, a router, wireless access, DNS/DHCP services, and an internet connection. Identify which device or layer owns the function and what evidence you would inspect to verify it.

What to check

  • Identify which OSI/TCP-IP layer and device type are primarily responsible.
  • Check configuration, interface or service state, counters, logs, and a simple end-to-end test.
  • Verify both normal operation and one realistic failure case so you understand what changes when the feature breaks.
Practice: Practice: explain Multiple WAN Circuits without reading the definition. Then draw or describe one network where it is used, name one failure symptom, and list the first two checks you would perform.

35.6 Application-Aware Routing

Application-Aware Routing affects how Layer 3 devices choose a path toward destination networks. Correct routing depends on the destination prefix, route source, next hop or exit interface, route preference, metric, and reachability of the next step.

Example: a router receives a packet for 10.20.30.40 and has several matching routes. It selects the most specific matching prefix, then forwards toward the route's next hop or exit interface if that path is usable.

What to check

  • Check the destination prefix and the most-specific matching route.
  • Verify next-hop reachability, route source, preference, metric, and return path.
  • Confirm that ACLs, NAT, VPN policy, or upstream routing are not blocking an otherwise-correct route.
Practice: Practice: explain Application-Aware Routing without reading the definition. Then draw or describe one network where it is used, name one failure symptom, and list the first two checks you would perform.

35.7 Dynamic Path Selection

PAT lets many inside hosts share one or a small number of public IPv4 addresses by tracking transport protocol and port mappings.

Example: place Dynamic Path Selection in a small office network containing clients, switches, a router, wireless access, DNS/DHCP services, and an internet connection. Identify which device or layer owns the function and what evidence you would inspect to verify it.

What to check

  • Identify which OSI/TCP-IP layer and device type are primarily responsible.
  • Check configuration, interface or service state, counters, logs, and a simple end-to-end test.
  • Verify both normal operation and one realistic failure case so you understand what changes when the feature breaks.
Practice: Practice: explain Dynamic Path Selection without reading the definition. Then draw or describe one network where it is used, name one failure symptom, and list the first two checks you would perform.

35.8 Latency Monitoring

Latency is the time required for traffic to travel between endpoints. Propagation, serialization, queueing, processing, and path choice can all contribute.

Example: place Latency Monitoring in a small office network containing clients, switches, a router, wireless access, DNS/DHCP services, and an internet connection. Identify which device or layer owns the function and what evidence you would inspect to verify it.

What to check

  • Confirm the symptom and determine whether the problem affects one host, one segment, one site, or many sites.
  • Compare actual configuration and measurements with the intended design, baseline, or documentation.
  • Change one variable at a time, verify the result, and document both the cause and the final fix.
Practice: Practice: explain Latency Monitoring without reading the definition. Then draw or describe one network where it is used, name one failure symptom, and list the first two checks you would perform.

35.9 Jitter Monitoring

Jitter is variation in packet delay. Real-time voice and video are especially sensitive to excessive delay variation.

Example: place Jitter Monitoring in a small office network containing clients, switches, a router, wireless access, DNS/DHCP services, and an internet connection. Identify which device or layer owns the function and what evidence you would inspect to verify it.

What to check

  • Confirm the symptom and determine whether the problem affects one host, one segment, one site, or many sites.
  • Compare actual configuration and measurements with the intended design, baseline, or documentation.
  • Change one variable at a time, verify the result, and document both the cause and the final fix.
Practice: Practice: explain Jitter Monitoring without reading the definition. Then draw or describe one network where it is used, name one failure symptom, and list the first two checks you would perform.

35.10 Packet-Loss Monitoring

Packet-Loss Monitoring is one of the core topics in SD-WAN. Understand what the term represents, where it operates in the network, what information it uses, and what observable behavior confirms that it is working correctly.

Example: place Packet-Loss Monitoring in a small office network containing clients, switches, a router, wireless access, DNS/DHCP services, and an internet connection. Identify which device or layer owns the function and what evidence you would inspect to verify it.

What to check

  • Confirm the symptom and determine whether the problem affects one host, one segment, one site, or many sites.
  • Compare actual configuration and measurements with the intended design, baseline, or documentation.
  • Change one variable at a time, verify the result, and document both the cause and the final fix.
Practice: Practice: explain Packet-Loss Monitoring without reading the definition. Then draw or describe one network where it is used, name one failure symptom, and list the first two checks you would perform.

35.11 SLA-Based Path Selection

PAT lets many inside hosts share one or a small number of public IPv4 addresses by tracking transport protocol and port mappings.

Example: place SLA-Based Path Selection in a small office network containing clients, switches, a router, wireless access, DNS/DHCP services, and an internet connection. Identify which device or layer owns the function and what evidence you would inspect to verify it.

What to check

  • Identify which OSI/TCP-IP layer and device type are primarily responsible.
  • Check configuration, interface or service state, counters, logs, and a simple end-to-end test.
  • Verify both normal operation and one realistic failure case so you understand what changes when the feature breaks.
Practice: Practice: explain SLA-Based Path Selection without reading the definition. Then draw or describe one network where it is used, name one failure symptom, and list the first two checks you would perform.

35.12 Encryption

Encryption is one of the core topics in SD-WAN. Understand what the term represents, where it operates in the network, what information it uses, and what observable behavior confirms that it is working correctly.

Example: place Encryption in a small office network containing clients, switches, a router, wireless access, DNS/DHCP services, and an internet connection. Identify which device or layer owns the function and what evidence you would inspect to verify it.

What to check

  • Identify which OSI/TCP-IP layer and device type are primarily responsible.
  • Check configuration, interface or service state, counters, logs, and a simple end-to-end test.
  • Verify both normal operation and one realistic failure case so you understand what changes when the feature breaks.
Practice: Practice: explain Encryption without reading the definition. Then draw or describe one network where it is used, name one failure symptom, and list the first two checks you would perform.

35.13 Branch Connectivity

Branch Connectivity is one of the core topics in SD-WAN. Understand what the term represents, where it operates in the network, what information it uses, and what observable behavior confirms that it is working correctly.

Example: place Branch Connectivity in a small office network containing clients, switches, a router, wireless access, DNS/DHCP services, and an internet connection. Identify which device or layer owns the function and what evidence you would inspect to verify it.

What to check

  • Identify which OSI/TCP-IP layer and device type are primarily responsible.
  • Check configuration, interface or service state, counters, logs, and a simple end-to-end test.
  • Verify both normal operation and one realistic failure case so you understand what changes when the feature breaks.
Practice: Practice: explain Branch Connectivity without reading the definition. Then draw or describe one network where it is used, name one failure symptom, and list the first two checks you would perform.

35.14 Local Internet Breakout

Local Internet Breakout is one of the core topics in SD-WAN. Understand what the term represents, where it operates in the network, what information it uses, and what observable behavior confirms that it is working correctly.

Example: place Local Internet Breakout in a small office network containing clients, switches, a router, wireless access, DNS/DHCP services, and an internet connection. Identify which device or layer owns the function and what evidence you would inspect to verify it.

What to check

  • Identify which OSI/TCP-IP layer and device type are primarily responsible.
  • Check configuration, interface or service state, counters, logs, and a simple end-to-end test.
  • Verify both normal operation and one realistic failure case so you understand what changes when the feature breaks.
Practice: Practice: explain Local Internet Breakout without reading the definition. Then draw or describe one network where it is used, name one failure symptom, and list the first two checks you would perform.

35.15 Failover

Failover is one of the core topics in SD-WAN. Understand what the term represents, where it operates in the network, what information it uses, and what observable behavior confirms that it is working correctly.

Example: place Failover in a small office network containing clients, switches, a router, wireless access, DNS/DHCP services, and an internet connection. Identify which device or layer owns the function and what evidence you would inspect to verify it.

What to check

  • Identify which OSI/TCP-IP layer and device type are primarily responsible.
  • Check configuration, interface or service state, counters, logs, and a simple end-to-end test.
  • Verify both normal operation and one realistic failure case so you understand what changes when the feature breaks.
Practice: Practice: explain Failover without reading the definition. Then draw or describe one network where it is used, name one failure symptom, and list the first two checks you would perform.

35.16 SD-WAN Controllers

SD-WAN uses centralized policy and an overlay to steer application traffic across multiple WAN transports according to availability, latency, loss, jitter, and business intent.

Example: place SD-WAN Controllers in a small office network containing clients, switches, a router, wireless access, DNS/DHCP services, and an internet connection. Identify which device or layer owns the function and what evidence you would inspect to verify it.

What to check

  • Identify which OSI/TCP-IP layer and device type are primarily responsible.
  • Check configuration, interface or service state, counters, logs, and a simple end-to-end test.
  • Verify both normal operation and one realistic failure case so you understand what changes when the feature breaks.
Practice: Practice: explain SD-WAN Controllers without reading the definition. Then draw or describe one network where it is used, name one failure symptom, and list the first two checks you would perform.

35.17 SD-WAN Security

SD-WAN uses centralized policy and an overlay to steer application traffic across multiple WAN transports according to availability, latency, loss, jitter, and business intent.

Example: place SD-WAN Security in a small office network containing clients, switches, a router, wireless access, DNS/DHCP services, and an internet connection. Identify which device or layer owns the function and what evidence you would inspect to verify it.

What to check

  • Identify the trust boundary and the traffic that should be permitted or denied.
  • Check authentication, authorization, encryption, policy order, logs, and time synchronization.
  • Verify the control with an allowed test and a denied test so policy behavior is observable.
Practice: Practice: explain SD-WAN Security without reading the definition. Then draw or describe one network where it is used, name one failure symptom, and list the first two checks you would perform.

35.18 SD-WAN Advantages

SD-WAN uses centralized policy and an overlay to steer application traffic across multiple WAN transports according to availability, latency, loss, jitter, and business intent.

Example: place SD-WAN Advantages in a small office network containing clients, switches, a router, wireless access, DNS/DHCP services, and an internet connection. Identify which device or layer owns the function and what evidence you would inspect to verify it.

What to check

  • Identify which OSI/TCP-IP layer and device type are primarily responsible.
  • Check configuration, interface or service state, counters, logs, and a simple end-to-end test.
  • Verify both normal operation and one realistic failure case so you understand what changes when the feature breaks.
Practice: Practice: explain SD-WAN Advantages without reading the definition. Then draw or describe one network where it is used, name one failure symptom, and list the first two checks you would perform.

35.19 SD-WAN Limitations

SD-WAN uses centralized policy and an overlay to steer application traffic across multiple WAN transports according to availability, latency, loss, jitter, and business intent.

Example: place SD-WAN Limitations in a small office network containing clients, switches, a router, wireless access, DNS/DHCP services, and an internet connection. Identify which device or layer owns the function and what evidence you would inspect to verify it.

What to check

  • Identify which OSI/TCP-IP layer and device type are primarily responsible.
  • Check configuration, interface or service state, counters, logs, and a simple end-to-end test.
  • Verify both normal operation and one realistic failure case so you understand what changes when the feature breaks.
Practice: Practice: explain SD-WAN Limitations without reading the definition. Then draw or describe one network where it is used, name one failure symptom, and list the first two checks you would perform.

35.20 SD-WAN Troubleshooting

SD-WAN uses centralized policy and an overlay to steer application traffic across multiple WAN transports according to availability, latency, loss, jitter, and business intent.

Example: place SD-WAN Troubleshooting in a small office network containing clients, switches, a router, wireless access, DNS/DHCP services, and an internet connection. Identify which device or layer owns the function and what evidence you would inspect to verify it.

What to check

  • Confirm the symptom and determine whether the problem affects one host, one segment, one site, or many sites.
  • Compare actual configuration and measurements with the intended design, baseline, or documentation.
  • Change one variable at a time, verify the result, and document both the cause and the final fix.
Practice: Practice: explain SD-WAN Troubleshooting without reading the definition. Then draw or describe one network where it is used, name one failure symptom, and list the first two checks you would perform.

Chapter 35 Review Questions

1. What should you remember about SD-WAN Overview?

Answer: SD-WAN uses centralized policy and an overlay to steer application traffic across multiple WAN transports according to availability, latency, loss, jitter, and business intent.

2. What should you remember about WAN Overlay?

Answer: WAN Overlay is one of the core topics in SD-WAN. Understand what the term represents, where it operates in the network, what information it uses, and what observable behavior confirms that it is working correctly.

3. What should you remember about Multiple WAN Circuits?

Answer: Multiple WAN Circuits is one of the core topics in SD-WAN. Understand what the term represents, where it operates in the network, what information it uses, and what observable behavior confirms that it is working correctly.

4. What should you remember about Dynamic Path Selection?

Answer: PAT lets many inside hosts share one or a small number of public IPv4 addresses by tracking transport protocol and port mappings.

5. What should you remember about Jitter Monitoring?

Answer: Jitter is variation in packet delay. Real-time voice and video are especially sensitive to excessive delay variation.

6. What should you remember about Encryption?

Answer: Encryption is one of the core topics in SD-WAN. Understand what the term represents, where it operates in the network, what information it uses, and what observable behavior confirms that it is working correctly.

7. What should you remember about Local Internet Breakout?

Answer: Local Internet Breakout is one of the core topics in SD-WAN. Understand what the term represents, where it operates in the network, what information it uses, and what observable behavior confirms that it is working correctly.

8. What should you remember about SD-WAN Controllers?

Answer: SD-WAN uses centralized policy and an overlay to steer application traffic across multiple WAN transports according to availability, latency, loss, jitter, and business intent.

9. What should you remember about SD-WAN Advantages?

Answer: SD-WAN uses centralized policy and an overlay to steer application traffic across multiple WAN transports according to availability, latency, loss, jitter, and business intent.

10. What should you remember about SD-WAN Troubleshooting?

Answer: SD-WAN uses centralized policy and an overlay to steer application traffic across multiple WAN transports according to availability, latency, loss, jitter, and business intent.