About Replication Servers
Replication servers are dedicated VXLAN tunnel endpoints (VTEPs) that are responsible for replicating Layer 2 broadcast, unknown unicast, and multicast (BUM) traffic. The VTEPs must send the BUM traffic to only one of the replication servers, which will then replicate it to all VTEPs in that virtual network identifier (VNID).
In Cisco NX-OS, replication servers are picked on a per-VNID basis. Therefore, all BUM traffic from a VNID is sent to this replication server.