Which control plane protocol is used between Cisco SD-WAN routers and vSmart controllers?

Overlay Management Protocol (OMP) is the proprietary control plane protocol for the Cisco SD-WAN fabric. It operates between the vSmart controllers and the WAN Edge routers (vEdge/cEdge), and also between the vSmart controllers themselves. OMP is responsible for distributing routing information (such as OMP routes, TLOC routes, and service routes), security keys for data plane encryption, and centralized data policies across the overlay network. It establishes and maintains the SD-WAN control plane, functioning similarly to BGP but is purpose-built for the overlay environment. All OMP communication occurs over secure DTLS or TLS connections.

A. OTCP: This is not a standard or recognized protocol within the Cisco SD-WAN architecture; it is a fictitious acronym used as a distractor.
C. UDP: UDP is a transport layer (Layer 4) protocol. While OMP control connections are encapsulated within DTLS, which runs over UDP (or TLS over TCP), UDP itself is the transport mechanism, not the control plane protocol.
D. BGP: BGP is a standard routing protocol used on the service-side (LAN) or transport-side (underlay) of a WAN Edge router to exchange routes with external networks, not for the overlay control plane between routers and vSmart controllers.

1. Cisco SD-WAN Design Guide: In the "Control Plane" section of the "Cisco SD-WAN Architecture" chapter, it states, "The vSmart controller is the centralized brain of the solution... It runs an OMP (Overlay Management Protocol) to communicate with the SD-WAN routers. OMP is the protocol responsible for establishing and maintaining the Cisco SD-WAN control plane." (Reference: Cisco SD-WAN Design Guide, Chapter: Cisco SD-WAN Architecture, Section: Control Plane).

2. Cisco SD-WAN Overlay Management Protocol (OMP) Configuration Guide, Cisco IOS XE Release 17.x: The introduction clearly defines the protocol's role: "The Overlay Management Protocol (OMP) is the control protocol that runs between Cisco vSmart Controllers and WAN Edge routers in the overlay network. The protocol is enabled by default. You do not need to explicitly enable it on Cisco vSmart Controllers and WAN Edge routers." (Reference: Cisco SD-WAN Overlay Management Protocol (OMP) Configuration Guide, Cisco IOS XE Release 17.x, Document ID: bcgompxe-17, Chapter: Overlay Management Protocol Overview).

3. Cisco SD-WAN Getting Started Guide: This guide explains the function of each component, stating, "The Cisco vSmart Controller is the centralized brain of the Cisco SD-WAN solution... It runs the Overlay Management Protocol (OMP) and distributes connectivity and policy information to the WAN Edge routers." (Reference: Cisco SD-WAN Getting Started Guide, Chapter: Cisco SD-WAN Overlay Network, Section: Cisco vSmart Controller).