GRE Tunneling is a new routing protocol developed by Cisco Systems, which enables packet data to be exchanged over any network interface. The original GRE is a modular routing protocol designed by Ethernet engineering teams at Bell Labs in the early 1980's. The major difference between the original and modern day GRE protocol is the use of the metric system in all the exchanged packets. The original GRE algorithm has been improved since its inception and allows for much more efficient data forwarding for both hosts and routers. Today, GRE stands for Generalized Domain Traffic and is used for IP-based packet filtering, data forwarding and security within the larger Bell Labs networking systems.
One aspect of this technology is the encapsulation of the normal ICMP signaling along with the header information to form a complete GRE tunnel interface. This technology is usually referred to as a GTP (Grambling Transport) or BIND (Border router Interchange) in industry. In simple terms, a GTP will forward packets of data through an IP-based service without concern for the MAC address or even sending of the packet through the standard Ethernet switch. This makes it possible to create large packets of data and transmit them as if they were to be sent directly to the destination device. It is also much more efficient than using the normal IP-based packets, as it is able to avoid dropping any of the incoming packets along the way as it does not use the normal hop by hop method.
An IP-based service can use either the GRE tunneling or BIND technology. The classic GRE is used when there is only one way to send a packet of data from a local computer to a remote destination. BIND on the other hand, is used when more than one path can be used to send the packet of data to the destination. With BIND, the network can handle multiple path options for a single destination address. The major difference between a GRE and BIND is that GRE uses the full IP address of the sender while BIND uses the part of the IP address of the sender only.
The two major types of GRE are Border network and Independent tunneling. A number of companies have utilized the two examples of GRE tunneling. An independent method is also known as independent private line connections (IP-pipe) that is used to connect two sites with the use of a private network of communication. There are basically two ways to use this kind of system. One can establish a private tunnel between the two sites and secondly, the client can gain access to the internet services at both the sites.
This means that in case one site has an address and the other does not, the latter is considered the 'gateway' for the purpose of passing the packet of data from the source to the latter. This is why it is also referred to as a Static Default Route. The 'gateway' or 'static default route' of a GRE tunneling system ensures that an IP packet will be sent from one gateway to another by default without the need to modify the IP settings. Another great thing about this kind of system is that the destination site will be able to determine or alter the destination IP by changing the gateway. Hence, you don't have to configure anything on your end.
But the above describes just one mode of operation of a GRE tunnel. The other mode of operation is known as encapsulation. Here, the physical layer 2 Ethernet cards of the source devices are configured such that they can pass through the output interface of the GRE. The output of the interface can be forwarded to any other interface or router, which is configured to accept forwarding information. Hence, the physical layer 2 Ethernet cards are also called 'emulated' or 'cloned' Ethernet cards.
The other kind of tunneling is also referred to as an example topology. In this case, there is a single physical interface and one logical layer, which is used to pass the message or data between the input and the output. An example topology for the GRE is given below:
The above details describe the operation of a GRE tunnel. By using the appropriate hardware, you can create the GRE tunnels or 'example topologies' for efficient session delivery. However, creating tunnels using the above described method is not without risks. If the traffic in the input goes out of control, the whole process will stop abruptly. Therefore, it is advisable to use 'bundle' or 'prox' routing, where many incoming packets are allowed to collide on the way to the final destination.
Generic Routing Encapsulation (GRE) is a routing protocol developed by Cisco Systems, which essentially can encapsulate an incredibly wide spectrum of networking technology within very small point-to-point connections or multipoint links on an Ethernet network.
This technology is quite capable of concealing all of the traffic that flows through any Ethernet device and is an ideal solution for many security applications.
GRE tunneling can help you manage all of the traffic that is going to or leaving your company.
There are no more firewalls that need to be installed and taken down every time you want to upgrade your security measures.
The concept behind a GRE tunnel is rather simple.
Any packets that are sent and received will use this unique IP address.
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