1.2 Explain the working principles of the Cisco Catalyst SD-WAN solution

What this section tests

Catalyst Software-Defined WAN (SD-WAN) is a WAN overlay architecture. WAN Edge routers build encrypted tunnels across transports like MPLS, broadband Internet, and LTE. Central controllers handle onboarding, control-plane exchange, management, and policy.

Note: Do not reduce SD-WAN to "uses the Internet." The exam tests centralized policy and transport-independent forwarding.

The four planes

Branch WAN Edge                         Controllers (cloud or on-prem)
+------------------+                  +---------------------------+
| Service VPN      |                  | Manager: templates/monitor|
| (user traffic)   |                  | Validator: onboarding     |
|        |         |   control (OMP)  | Controller: routes/policy |
| Transport VPN    |<---------------->|                           |
| MPLS + Internet  |   data tunnels   +---------------------------+
+------------------+                  BFD measures tunnel health

Terms that matter

• TLOC: a transport locator. It is the system IP, color, and encapsulation that reach a WAN Edge on one transport.
• OMP: the control protocol between WAN Edges and Controllers. It carries routes, TLOCs, and policy.
• BFD: Bidirectional Forwarding Detection. It measures tunnel liveliness, loss, latency, and jitter.
• VPN: a segmentation container. VPN 0 is the transport side. Service VPNs carry user networks.

Recognition commands

show sdwan control connections
show sdwan omp peers
show sdwan omp routes
show sdwan bfd sessions
show sdwan app-route stats
show sdwan tunnel statistics

Lab: explain the overlay

Draw two branches. Give each branch two transports: MPLS and Internet. Put one subnet behind each branch.

Answer these questions before you type commands:

1. Which interface belongs to the transport VPN?
2. Which routes are local service-side routes?
3. Which controller distributes reachability?
4. Which tunnels carry user traffic?
5. What changes when the Internet circuit has high loss and MPLS is clean?

Then verify with the control, route, and tunnel commands. The goal is to connect each show output to one plane.

Pass check

You are ready when you can do these things:

• Name the component for templates, onboarding, OMP routes, and encrypted tunnels.
• Explain what still works when each controller is unreachable.
• Connect each show sdwan command to one plane.