GRE Fullform

GRE or Generic Routing Encapsulation is a tunneling protocol developed by Cisco. It encapsulates IP packets i.e. deliverable inner packets into outer packets. It transports them to a device that de-encapsulates them and routes them to their final destination, over a network. Characteristics:

• GRE is a routing encapsulating protocol.
• GRE provides a stateless, private connection.
• GRE protocol creates a point-to-point connection similar to Virtual Private Network(VPN).
• It uses logical hub-and-spoke topology.
• It can carry any OSI layer 3 protocols over an IP network.
• GRE provides communication between two hosts of different private networks by building a tunnel between two routers over the Internet.
• The GRE connection endpoints can be terminated with the help of Virtual Tunnel Interface (VTI) present in each device.

Advantages:

• GRE protocol supports encapsulating IPv4 broadcast and multicast traffic. It also supports IPv6.
• GRE is a simple and flexible protocol.
• GRE tunnel encapsulates multiple protocols under a single protocol.
• GRE can also route non-TCP/IP protocols such as IPX or AppleTalk through an IP network.
• GRE protocol can connect multiple discontinuous sub-networks.
• GRE protocol allows you to set up a Virtual Private Network (VPN) over the Wide Area Network (WAN).
• GRE protocol can also work easily with networks having limited hops.
• GRE protocol is easy to debug.

Disadvantages:

• GRE protocol does not provide a Data encryption facility i.e. network security is not guaranteed. It needs to be integrated with other secure tunneling protocols such as IPSec to provide network security.
• GRE protocol is less scalable as defining GRE tunnels is a manual task.