Note: For more information about the GRE protocol, see Understanding the generic routing encapsulation protocol (GRE).
The current version of LCOS provides a number of "Ethernet over GRE" tunnels (EoGRE) to transmit Ethernet packets via GRE. Since these Ethernet packets move on OSI layer 2 only, the EoGRE tunnel only functions as a bridge.
This can be used to implement L2VPN (VPN as a simple level-2 bridge) or a transparent Ethernet bridge over WAN.