What Is the Function of the Tunnel Interface (GRE Interface)? What Are the Tunnel Source Interface and Tunnel Destination Interface?
The tunnel interface (GRE interface) encapsulates and decapsulates data packets using GRE. The tunnel interface that sends encapsulated packets is called the tunnel source interface, and the one that receives these packets on the peer end is called the tunnel destination interface.
Generally, the local WAN interface is used as the tunnel source interface, and the peer WAN interface is used as the tunnel destination interface.