MTU – Maximum transmission unit is the size of e largest protocol unit that can be communicated in a single network-layer it is usually associated with network interfaces. Setting up the tunnel interface IPs and provide public IP addresses for both ends of the GRE tunnel. The new packet will look something like this: Now we created a “tunnel” for data packets that might have an issue reaching their destination in their original form. How does the GRE Tunnel work?įirst, we must configure the 2 endpoints – Routers to send and receive GRE packets, all the other routers in the underlying network will not open the packet that the GRE Protocol encapsulated meaning they will not look inside as they assume the content is just the data payload that is redundant. So when the package gets to its destination router he will unpack the original envelop and push it to its original and final receipt. A great analogy is taking an envelope that you were about to send and wrapping it in another envelope. For example, using IPV6 in an IPV4 network. When using GRE we can therefore switch protocols and use protocols that are not used by the underlying network in our original packet, by wrapping the protocol that is not in use with a protocol that the underlying network understands. Mainly for giving us a direct road (route) through the network from one endpoint to another. Generic routing encapsulation is a tunneling protocol created by Cisco, The purpose of this protocol is to encapsulate a data packet that is being used by one protocol within another data packet.

What is gre tunnel