# SD-WAN Interview Q&A: Key Concepts and Technical Deep Dive

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Cisco Catalyst SD-WAN is a transformative approach to wide-area networking, offering centralized control, enhanced security, and improved performance. Below, we explore key SD-WAN concepts along with practical commands and configurations to solidify your understanding.

SD-WAN Control Components

1. SD-WAN Controller: Manages overlay network policies.

2. SD-WAN Validator: Authenticates and authorizes SD-WAN components.

3. SD-WAN Manager: Provides monitoring, troubleshooting, and configuration.

You Should Know:

🔹 Verify Control Plane Status (CLI):

show sdwan control connections 
show sdwan control connections-history

🔹 **Check vSmart Connections**:

show sdwan control local-properties

## **SD-WAN Manager Functions**

  • Troubleshooting (🔍): 
    show sdwan app-route stats 
show sdwan bfd sessions
  • Monitoring (📊): 
    show sdwan interface 
show sdwan tunnel statistics

## **WAN Edge Data Plane Encryption**

SD-WAN uses **IPsec** for secure traffic encapsulation.

### **You Should Know:**

🔹 **Verify IPsec Tunnels**:

show sdwan ipsec inbound-connections 
show sdwan ipsec outbound-connections

🔹 **Debug IPsec Negotiation**:

debug sdwan ipsec error 
debug sdwan ipsec info

## **SD-WAN Validator & NAT Traversal**

The Validator ensures secure component authentication and handles NAT traversal.

### **You Should Know:**

🔹 **Check NAT Status**:

show sdwan control nat translations

🔹 **Force NAT Refresh**:

clear sdwan control nat-translations

## **Multi-Tenancy & Segmentation**

Cisco SD-WAN supports **multi-tenancy** and **per-VPN topologies**.

### **You Should Know:**

🔹 **View VPN Segmentation**:

show sdwan vpn 
show sdwan policy from-vsmart

🔹 **Modify VPN Policies**:

config-transaction 
policy 
vpn-list VPN10 
sequence 10 
match source-ip 10.1.1.0/24 
action accept 
commit

## **BFD for Performance Metrics**

Bidirectional Forwarding Detection (BFD) measures:

  • Delay (⏳)
  • Loss (📉)
  • Jitter (📡)

### **You Should Know:**

🔹 **Check BFD Sessions**:

show sdwan bfd sessions

🔹 **Adjust BFD Timers**:

bfd slow-timer 1000 
bfd multiplier 7

## **Unsupported Routing Protocols**

  • EIGRP ❌
  • RIPv1 ❌

### **You Should Know:**

🔹 **Preferred Protocols**:

router ospf 100 
network 192.168.1.0 0.0.0.255 area 0

🔹 **BGP Configuration**:

router bgp 65001 
neighbor 203.0.113.1 remote-as 65002

## **Deployment Options**

  • Cisco Cloud Hosted ☁️
  • Customer On-Premises 🏢
  • Partner Cloud Hosted ☁️

### **You Should Know:**

🔹 **On-Prem vManage Setup**:

vmanage# show system status 
vmanage# request ntp sync

# **What Undercode Say**

SD-WAN revolutionizes network management by decoupling control and data planes, enabling dynamic traffic steering, and improving security with IPsec. Key takeaways:
– Use show sdwan control connections to verify controller status.
– IPsec ensures encrypted WAN traffic (debug sdwan ipsec for troubleshooting).
– BFD is critical for real-time performance monitoring.
– Multi-tenancy allows segmented VPN topologies (show sdwan vpn).
– Avoid EIGRP/RIPv1—use OSPF/BGP instead.

For deeper learning:

# **Expected Output:**

A structured guide with actionable CLI commands and SD-WAN best practices.

References:

Reported By: Breeze Singh – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅

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