GRE Tunnel

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What is a GRE Tunnel?

A GRE (Generic Routing Encapsulation) tunnel is a protocol developed by Cisco that encapsulates a wide variety of network layer protocols inside virtual point-to-point links over an IP network. Essentially, it allows for the creation of a private, secure, and isolated path between two endpoints over a public or untrusted network, like the Internet.

Why is it Used?

GRE tunnels are used for several reasons:

  1. Protocol Encapsulation: GRE can encapsulate a variety of network layer protocols, enabling the transport of protocols that might not be natively supported by the underlying network.
  2. Multicast Traffic: Unlike some other tunneling protocols, GRE supports multicast traffic, making it suitable for dynamic routing protocols.
  3. Simplified Connectivity: It simplifies the setup of VPNs and other network connections by creating a virtual point-to-point link.
  4. Interoperability: GRE is defined in RFC 2784, making it widely supported across different vendors.

Pros and Cons

Pros:

Cons:

Basic GRE tunnel Lab:

Goal: Ping Loopbacks present at R1 and R4 using GRE tunnel.

GRE tunnels are used to encapsulate IP packets and send it over the public domain.

Important Points:

·         GRE is default type of a tunnel encapsulation. 

·         The IP packet is encapsulated with the GRE Header, tunnel destination/source IP header and sent over the public domain.

·         Not secure, as it is clear text.

Conditions for GRE Tunnel to work:

·         Tunnel source and destination should be valid and reachable.

·         Tunnel should have an IP address

This lab illustrates the concept in simple way.

Lab Doc and Script file.


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