Generic Routing Encapsulation (GRE) is a protocol that encapsulates packets of some network layer protocols, such as Internetwork Packet Exchange (IPX), IPv6, and AppleTalk. GRE allows encapsulated packets to be transmitted through a different network layer protocol, such as IPv4.
As a Layer 3 tunneling technology, GRE encapsulates packets of one protocol into packets of another protocol and transparently transmits them over tunnels. This enables packet transmission on heterogeneous networks.
GRE is easy to implement and increases only a few loads on devices at both ends of a tunnel.
GRE sets up tunnels over an IPv4 network to connect networks running different protocols, reusing the original network structure and reducing costs.
GRE enlarges the operation scope of network protocols that support limited hop counts, allowing for flexible topologies on enterprise networks.
GRE connects discontiguous subnets and sets up virtual private networks (VPNs) to ensure secure connections between enterprise headquarters and branches.