OMP is the heart of the Cisco SD-WAN overlay routing solution. It runs inside of our DTLS control plane connections and forms a peering relationship between WAN Edges and vSmart Controllers and between vSmarts. It is not used between vEdge devices. The diagram below depicts these peering relationships.
Note that OMP peerings are never made between our WAN edge devices. This once again highlights our separation of control and data plane in the SD-WAN architecture.
OMP is a propriety protocol that is enabled by default in our Transport VPN (VPN0), so you do not need to configure anything to make it come up. As soon as our DTLS connections to our vSmart are established our OMP peerings will automatically be formed.
OMP peering(s) are formed between the system-IP of the two devices, and the protocol is responsible for the advertising service side prefixes and associated VPNs, data plane security parameters, overlay routing policy and transport network location mappings. As you can see from this list OMP does a lot more than your traditional routing protocol.
It is used to exchange routing, reachability for TLOCs, unicast/multicast destinations, service routes, BFD up/down states, security, policies and cloud on ramp for SaaS probe stats throughout the fabric. It also distributes the encryption IPSEC keys and data and app aware policies. If OMP is down that means control plane is down for that vEdge.