GRE Tunneling is a framing protocol developed by Cisco Systems, which enables networks to use full advantage of the VPN (Virtual Private Network). The VPN is used to secure sensitive sites and information from unauthorized access on the internet. An example of a VPN is the Starbucks mobile application that protects mobile numbers from being used for dialing telephone numbers. Another major issue with public networks is port blocking, which is caused when multiple protocols try to access the same port. GRE will prevent these protocols from using that port. GRE also offers security benefits such as port encryption.
The major benefit of the VPN technology is to provide secure, protected communication between two or more endpoints. The process is called GRE encapsulation and it provides a flexible means of tunneling data packets through a private network of routers. The basic premise of the tunneling is to create a virtual private network within a private physical network by forwarding traffic between multiple gateway IP addresses. It achieves this by the application of a small network of tunnels where all the data packets are sent.
To explain further, there are four types of GRE options, namely, LSI (Layer 2 Switch Ethernet), STP (Subnet Reverse Flow) and BPD (Border Gateway Protocol). STP uses the existing Ethernet layer for its transport; whereas LSI uses the layer 1 network on the client side and STP uses the layer 3 on the server side. There are some advantages of using GRE over other options. First and foremost, it provides a transparent Local Area Network for a Wide Area Network. Another important benefit is the tunnel source router does not need to reconfigure to receive the packets. The reason for this is that the negotiation takes place in the form of an encapsulated payload.
One of the benefits of using GRE over STP is that it supports reliable fast convergence. The forwarding path does not change regardless of the traffic load because both the users decide how fast they want to converge and then get to do so. In addition, the number of hop-up approaches can be increased without affecting the performance of the GRE. Furthermore, in case of EDGE or bidirectional routing encapsulation, no rewriting of the packets needs to occur because both the directions can use the same initial IP address. However, in the case of GRE over Ethernet, the process of rewriting is done at the layer level of the network adapter to make a connection to another GRE device.
There is also a very simple method called BSD forwarding. This is a simple way of performing the forwarding of packets, which saves a considerable amount of time. For BSD, the first user data packet is received and the destination field is set. After this the second user data packet is received and it has to be set as well. On the other hand, the first user data packet of an EoE group is not sent, but the destination is set to the reserved or global port of the EoE group. This group will forward its packets to other groups within the EoE group.
The big advantage of using GRE Tunnel over STP is that it saves time and improves reliability. This is the reason why GRE is used for point to point Tunneling Protocol (TPL). However, there are many disadvantages too, which needs to be considered before adopting GRE over Ethernet.
The biggest disadvantage of the tunnel interface is that it has to deal with some very busy networks. There is no support for BSD forwarding because this protocol is used in a private local area network (LAN), which cannot be tied-in to any main network. To answer this problem, the Novell developers added support for the concept of Local Area Networks (LANs) and Wide Area Networks (WANs). This feature makes the tunnel interface administratively more difficult to handle than STP.
Novell also offers several options for controlling and monitoring traffic on the network. Some of these features include auto discovery, BSD forwardings, and BSD-based firewall. It also offers two different kinds of firewall protection – blocking based on destination tunnels and public networks. In addition to these, Novell provides a web-based administration interface for controlling and monitoring all traffic on the network as well as controlling and accessing the various modules and services.