User`s guide

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Configuration - Network > Interfaces > GRE
Generic Routing Encapsulation (GRE) is a means of transporting IP packets from one device
to another through an unencrypted point-to-point IP tunnel. Multiple tunnels may be
configured to multiple devices. Below the GRE Interfaces sub menu you will find the
individual tunnel configuration. When configured, a GRE tunnel will be created between 2
devices.
Configuration - Network > Interfaces > GRE > Tunnel n
Description:
This parameter allows you to enter a name for this GRE instance, to make it easier to
identify it.
IP address:
This is the IP address of the virtual interface that will be used by the tunnel. This parameter
is used in conjunction with the mask parameter below. This parameter MUST be entered for
the tunnel to work.
Mask:
Used with the IP address parameter to clarify the subnet in use on the virtual interface. This
would normally be a 30 bit mask as this is a point-to-point link (255.255.255.252).
Source IP Address:
The two sub options here will allow you to specify a source address either from a specified
interface or by manually assigning an address. If you do not select either option the default
address for the route the packet leaves the router through will be used (please note that if
the interface through which the GRE packets exit does not have natting turned on then the
default router address will be used – by default this will be the Ethernet 0 address).
Use Interface:
These 2 parameters allow you to select the GRE tunnel source interface, so the tunnel
end point can be a physical interface rather than a virtual IP address. This is for using
GRE without IPSec. These parameters should not be used if the source address is used
in the parameter below. Select from the drop down boxes the available interface type
and number.
Use IP Address:
A virtual host IP address for the local end of the tunnel, configured for routing purposes.
This IP address has no other use and needs no mask as it is a host address. e.g. 1.1.1.1.
This option is normally used in conjunction with IPSec. This parameter should not be
used if the interface is selected as the source using the “Use Interface” options above.
Destination IP Address or Hostname:
This is the FQDN or IP address of the remote end of the tunnel. This could also be the
virtual host IP address for the remote end of the tunnel, configured for routing purposes.
e.g. 2.2.2.2
Enable keepalives on this GRE tunnel
Selecting this checkbox will display the GRE keepalive parameters. Keepalives are needed
so allow the router to determine whether the tunnel interface is receiving traffic correctly or
not. If keepalives fail, the tunnel will be marked as down.