GRE Tunnels
You can use generic routing encapsulation (GRE) as the carrier protocol for a variety of passenger protocols.
The following figure shows the IP tunnel components for a GRE tunnel. The original passenger protocol packet becomes the GRE payload and the device adds a GRE header to the packet. The device then adds the transport protocol header to the packet and transmits it.
![](/c/dam/en/us/td/i/100001-200000/180001-190000/185001-186000/185053.eps/_jcr_content/renditions/185053.jpg)