GRE (Generic Routing Encapsulation) is a tunneling protocol developed by Cisco Systems that can encapsulate a wide variety of network layer protocols inside virtual point-to-point links over an Internet Protocol network. The GRE Tunnel can be configured between any two devices that are compatible with this protocol.
From the point of view of the traffic transferred, the GRE tunnel is one hop.
There are 2 modes of GRE operation: TUN (Tunnel mode) or TAP (L2 transparent connection) with SW bridge. Implementation within RipEX only covers the TUN mode.
Packets passing through the GRE tunnel are not protected against loss and are not encrypted.
The GRE tunnel neither establishes nor maintains a connection with the peer. The GRE tunnel is created regardless of peer status (peer need not exist at all).
The GRE tunnel has its own IP address and mask. Network defined by this address and mask contains only 2 nodes – each end of the tunnel.
As the GRE tunnel adds an additional header, a lower MTU is set (1476 B) to prevent GRE packet fragmentation. Incoming packets may be fragmented within the GRE interface.
Packet acknowledgment and encryption (AES256) can be configured on the Radio channel. Both options are independent of GRE tunnels and apply to all the radio traffic.