What is the purpose of the Overlay Multicast TEP in a Cisco ACI Multi-Site deployment?

Unicast VXLAN data plane traffic is sourced and received by the Unicast TEPs (U-TEPs) on the leaf switches, not the Overlay Multicast TEP.

MP-BGP EVPN adjacencies are established by the Multi-Site Orchestrator and the Inter-Site Network (ISN) devices, typically the border leaf or spine nodes, using dedicated control plane mechanisms, not the OM-TEP.

While it involves multicast traffic, the OM-TEP's primary purpose is not just to encapsulate but specifically to perform head-end replication for BUM traffic to ensure efficient delivery across sites, which is a more specific and accurate description of its function.

The Overlay Multicast TEP (OM-TEP) in ACI Multi-Site is dedicated to handling Broadcast, Unknown Unicast, and Multicast (BUM) traffic. For BUM traffic that needs to traverse between sites, the OM-TEP at the source site performs head-end replication; it encapsulates the BUM traffic into a multicast group and sends it to the OM-TEPs at the destination sites, which then de-encapsulate and forward the traffic locally. This mechanism ensures efficient distribution of BUM traffic across the multi-site fabric without flooding unnecessary traffic to all leaf nodes directly.