Tunneling is a mechanism that makes transfer of payloads feasible
over an incompatible delivery network. It allows the network user to
gain access to denied or insecure networks. Data encryption may be
employed to transport the payload, ensuring that the encapsulated user
network data appears as public even though it is private and can easily
pass the conflicting network.

Generic routing encapsulation
(GRE)

Generic routing encapsulation (GRE) is a protocol that runs over IP
and is employed when delivery and payload protocols are compatible but
payload addresses are incompatible. For instance, a payload might think
it is running on a datalink layer but it is actually running over a
transport layer using datagram protocol over IP. GRE creates a private
point-to-point connection and works by encapsulating a payload. GRE is a
foundation protocol for other tunnel protocols but the GRE tunnels
provide only weak authentication.

Virtual extensible local area network (VXLAN)

The purpose of VXLAN is to provide scalable network isolation. VXLAN
is a Layer 2 overlay scheme on a Layer 3 network. It allows an overlay
layer-2 network to spread across multiple underlay layer-3 network
domains. Each overlay is termed a VXLAN segment. Only VMs within the
same VXLAN segment can communicate.

Generic
Network Virtualization Encapsulation (GENEVE)

Geneve is designed to recognize and accommodate changing capabilities
and needs of different devices in network virtualization. It provides a
framework for tunneling rather than being prescriptive about the entire
system. Geneve defines the content of the metadata flexibly that is
added during encapsulation and tries to adapt to various virtualization
scenarios. It uses UDP as its transport protocol and is dynamic in size
using extensible option headers. Geneve supports unicast, multicast, and
broadcast.