GRE tunnels support GRE over IP, GRE over OSPF, and GRE over IPSec VPN. Click Add to add a GRE tunnel, as shown in the following figure.

Tunnel No.: The number of the new tunnel port.

Zone: The zone where the outbound interface resides.

IP Address: The IP address of the new tunnel. The network segment where the IP address resides serves as the OSPF running segment.

Type: Specify the tunnel type, which can be IPv4 or IPv6.

Source Address: The actual source address of the WAN route of the outbound interface at the local end.

Destination Address: The actual destination address of the WAN route of the incoming interface at the peer end.

GRE Key: A shared key, which must be consistent at both ends.

Advanced: You can set IPv4 MTU, IPv6 MTU, Message Checksum, and Send Keepalive Message.

Click Save. The GRE tunnel is successfully set up.