Which technology reduces reliance on STP and transports both unicast and multicast traffic in modern data-center overlays?

VXLAN (Virtual Extensible LAN) is a tunneling protocol that encapsulates Layer 2 Ethernet frames within Layer 3 UDP packets, allowing for the creation of large-scale virtual networks over an existing IP infrastructure. This reduces reliance on STP by providing a loop-free underlay and enables the transport of both unicast and multicast traffic across the data center, making it ideal for modern overlay networks. VLANs are a Layer 2 technology with limitations in scale and do not address STP issues across large networks. VPC (Virtual Port Channel) is a Cisco-specific technology for multi-chassis EtherChannel, primarily for link redundancy and increased bandwidth, not for overlay networking or STP replacement across an entire data center. VSS (Virtual Switching System) combines two physical Catalyst switches into one logical switch, improving redundancy and simplifying management, but it's not an overlay technology that transports traffic across a data center fabric.