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What is Generic Routing Encapsulation (GRE) in networking?

gre in networking

Generic Routing Encapsulation (GRE) is a tunneling protocol that can encapsulate a wide variety of network layer protocols inside virtual point-to-point links over an Internet Protocol (IP) network. GRE in Networking is a key component of many VPNs and is also used to implement Virtual Private Network (VPN) tunneling. It is also used for tunneling other protocols such as Internetwork Packet Exchange (IPX) and AppleTalk.

GRE tunnels are configured on network routers and use IP addresses to route data packets between the tunnel endpoints. In this blog, we will learn what is GRE, how it works, the benefits and drawbacks of the GRE, and its uses. We will also learn what is the current scenario of the GRE and its future. 

In the previous blog of our CCNA 200-301 series , we talked about the WAN topologies. I recommend you go through it before you jump to this blog. 

Keep reading to learn more about GRE and how it is used in networking!

What is GRE?

Generic Routing Encapsulation (GRE) is a tunneling protocol designed to encapsulate network layer protocols inside virtual point-to-point links over an Internet Protocol network. In other words, GRE tunnels create a secure channel through which data can be sent between two locations, similar to a VPN connection. 

GRE tunnels are a logical link between two endpoints, such as two router interfaces. When a packet is sent over a GRE tunnel, the GRE tunnel encapsulates the data packets and adds a GRE header. The GRE header contains the following information:

  • The source and destination IP addresses, 
  • The GRE protocol identifier, and
  • A sequence number.

This information allows the endpoints to route data packets correctly. The GRE tunnel endpoint routers use this information to decapsulate the data packets and route them to the correct destination. 

GRE is a versatile protocol that can tunnel Layer 3 protocols such as IP, as well as IPX, AppleTalk, and DECnet protocols. 

GRE tunnels are stateless. This means that there is no information about the state or availability of the remote tunnel endpoint to the endpoint of the tunnel itself.

GRE is not a secure protocol, meaning that transmission of sensitive information is not recommended. To address this issue, GRE tunnels can be configured to provide authentication and encryption.

How does GRE work?

GRE tunneling works by performing two processes:

  • Encapsulation at the tunnel source.
  • De-capsulation at a tunnel remote router.

Encapsulation at the tunnel source:

  • GRE functions by encapsulating an inner packet that needs to be delivered to the destination network. 
  • It is encapsulated inside an outer IP network.

De-capsulation at the tunnel remote router:

  • When an IP packet is received by the destination switch, the outer IP header, and the GRE header. 
  • The encapsulation is removed when the packet reaches the tunnel endpoint. Then, the inner packet is carried forward to its final destination.
  • The inner header then decides where the packet needs to be routed.

What are the benefits of the GRE in Networking?

The following are the major benefits of GRE tunneling:

  • Versatility:

The primary benefit of the GRE is its versatility. GRE is capable of encapsulating a wide range of network layer protocols, including IP, IPX, AppleTalk, and DECnet protocols. This allows the same tunnel to carry different types of traffic, depending on the protocol used. 

  • Reliability:

In addition to being versatile, GRE is also reliable. By adding a GRE header to each packet sent over the tunnel, the tunnel endpoints can be confident that the data will reach its destination. This reliability makes GRE a great choice for packet tunneling. 

  • Authentication and encryption:

Finally, GRE tunnels can be configured to provide authentication and encryption. This ensures that data sent over the tunnel is secure and will not be tampered with.

Drawbacks of GRE

  • Lack of security:

One of the major drawbacks of the GRE is its lack of security. Without the use of authentication and encryption, GRE tunnels can be vulnerable to attack. 

  • Vulnerable:

Data sent over the tunnel is vulnerable to sniffing and other network-based attacks.

  • Scalable:

Another limitation of the GRE is its scalability. GRE tunnels are point-to-point, meaning they are not well-suited for large networks. This can make setting up large networks with multiple GRE tunnels difficult.

Who uses GRE in Networking?

GRE is used by many organizations and individuals for a variety of purposes. It is a common choice for setting up virtual private networks (VPNs) between multiple sites. 

It is also used to tunnel other protocols such as IPX and AppleTalk. 

GRE is also widely used by network engineers to perform troubleshooting, network simulation, and other network-related tasks. The ability to easily configure and modify GRE tunnels makes it a great tool for testing various network scenarios.

Where Does GRE Stand Today?

GRE is a type of tunnel that belongs to the WAN 2.0 technology and is one of the best ways to connect private networks across shared or public network infrastructure. You must note that tunnels do not provide any encryption. In short, it is a part of the traditional network routing model.

Thanks to SD-WAN, the new age WAN 3.0 technology is a collection of tunnels, often referred to as “virtual networks”. This has taken over the GRE tunneling technology as it supports multi-path routing.

What Is The Future of the GRE?

The interesting part is that the future networks would work without any WAN. There will be no need for tunnels, tags, etc. The networks will be able to provide secure packet routing from any private network to another private/public network through any IPv4 and IPv6 addresses.

The existing networks will remain the same but the routing process will become more efficient and intelligent.

Conclusion

Generic Routing Encapsulation (GRE) is a tunneling protocol that is able to package a large variety of network layer protocols inside virtual point-to-point links over an Internet Protocol (IP) network. 

GRE in Networking is a versatile protocol that is widely used by organizations, individuals, and network engineers alike. While GRE has many benefits such as its versatility and reliability, it also has some drawbacks such as its lack of security, and scalability issues when used in large networks. 

Despite its drawbacks, GRE remains a popular choice for tunneling protocols due to its ease of use and configurability.

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