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Industry Cellular Gateway
5.1.5 GRE
Generic Routing Encapsulation (GRE) is a tunneling protocol developed by Cisco Systems that encapsulates a
wide variety of network layer protocols inside virtual point-to-point links over an Internet Protocol
internetwork.
Deploy a M2M gateway for remote site and establish a virtual private network with control center by using
GRE tunneling. So, all client hosts behind M2M gateway can make data communication with server hosts
behind control center gateway.
GRE Tunneling is similar to IPSec Tunneling, client requesting the tunnel establishment with the server. Both
the client and the server must have a Static IP or a FQDN. Any peer gateway can be worked as either a client
or a server, even using the same set of configuration rule.
GRE Tunnel Scenario
To setup a GRE tunnel, each peer needs to
setup its global IP as tunnel IP and fill in the
other's global IP as remote IP.
Besides, each peer must further specify the
Remote Subnet item. It is for the Intranet of
GRE server peer. So, at GRE client peer, the
packets whose destination is in the dedicated
subnet will be transferred via the GRE tunnel.
Others will be transferred based on current
routing policy of the gateway at GRE client peer.
But, if you entered 0.0.0.0/0 in the Remote
Subnet field, it will be treated as a "Default
Gateway" setting for the GRE client peer, all
packets, including the Internet accessing of GRE
client peer, will go through the established GRE
tunnel. That means the remote GRE server peer controls the flow of any packets from the GRE client peer.
Certainly, those packets come through the GRE tunnel.
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