GRE Tunnel Fields
Name of the GRE tunnel.
Select the interface to use as the local GRE tunnel endpoint (source interface), which is an Ethernet interface or subinterface, an Aggregate Ethernet (AE) interface, a loopback interface, or a VLAN interface.
Select the local IP address of the interface to use as the tunnel interface address.
Enter the IP address at the opposite end of the GRE tunnel.
Select the Tunnel interface that you configured. (This interface identifies the tunnel when it is the next hop for routing.)
Enter the TTL for the IP packet encapsulated in the GRE packet (range is 1 to 255; default is 64).
Copy ToS Header
Select to copy the Type of Service (ToS) field from the inner IP header to the outer IP header of the encapsulated packets to preserve the original ToS information.
Select to enable the Keep Alive function for the GRE tunnel (disabled by default). If you enable Keep Alive, by default it takes three unreturned keepalive packets (Retries) at 10-second intervals for the GRE tunnel to go down, and it takes five Hold Timer intervals at 10-second intervals for the GRE tunnel to come back up.
Set the interval between keepalive packets that the local end of the GRE tunnel sends to the tunnel peer, and the interval that each Hold Timer waits after successful keepalive packets before the firewall re-establishes communication with the tunnel peer (range is 1 to 50; default is 10).
Set the number of intervals that keepalive packets are not returned before the firewall considers the tunnel peer to be down (range is 1 to 255; default is 3).
Set the number of intervals that keepalive packets are successful before the firewall re-establishes communication with the tunnel peer (range is 1 to 64; default is 5).