Generic Routing Encapsulation VPN or GRE Tunnel is a VPN networking technology developed by Cisco Systems, which can encapsulate a range of routing protocol-based networks within a virtual point-to-site or point-to-multipoint connections over an IP network. Generic Routing Encapsulation (GHE) can be considered the most generic form of VPN networking because it is intended to provide cost-effective and flexible solutions for routing through multiple layers of an Ethernet or other virtual LANs. A GRE tunnel enables the transport of IP packets on the Ethernet mesh to bypass Layer 2 routers, using the Ethernet header as a virtual tunnel. A GRE tunnel can be used to provide IP-based IP Multicast services such as VOIP or even WAN Wide Area Networks.
The Ethernet technology is an IP-based network networking solution that provides an IP-based routing and forwarding mechanism. It provides a single, secure connection between two or more devices in a local area network or the Internet. By default, Ethernet-based routing systems are able to route Ethernet packets to the nearest physical router that is in their immediate vicinity. In addition, it can be used as an extensible virtual private LAN (VPN) that is able to be used as a local area network (LAN), or an enterprise-class virtual private LAN (VPLS) that allows its customers to establish a high-speed high-availability VPN infrastructure in their enterprise. The VPLS is ideal for use in application-based virtual private LANs (VPNs) for applications such as file storage and remote desktop or web conferencing.
By utilizing GRE tunnel technology, an enterprise can create a more robust VPN that will allow for application-aware forwarding, which enables the VPN to be configured and managed with a comprehensive set of rules, while allowing for secure data transfer. There are several VPN vendors available that are offering GRE tunnel technology. The technology is most commonly available in virtual Private Branch Exchange (PBX) systems and in Wide Area Networks (WAN). It can also be used in enterprise-grade enterprise-class WAN VPNs. In both types of VPNs, an enterprise can use one virtual IP address, one or more virtual LAN addresses, or an entire virtual LAN to create a GRE tunnel and enable forwarding of IP packets to their destination IP addresses. GRE tunnel can also be used to enable a VPLS as a network access point, or as a gateway into an internal Ethernet network.