Digi TransPort User Manual page 99

GRE parameters
IP address
This is the IP address of the virtual interface that is 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
You can use this parameter 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 allows 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 two 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, such as 1.1.1.1. This
option is normally used in conjunction with IPSec. Do not use this parameter 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. such as
2.2.2.2
Enable keepalives on this GRE tunnel
Select this checkbox to 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 is marked as down.
Send a keepalive every s seconds
When configured to a non-zero value, keepalive packets is sent to the remote end of the
tunnel and the response is monitored to detect if the tunnel is up or down. If the tunnel is
detected as down, the routing table metric will be altered. Value is configured in seconds. If
this value is set to zero then keepalives will not be used.
Bring this GRE tunnel down after no replies to n keepalives
This parameter specifies the consecutive number of keepalive packets that need to fail before
the tunnel is detected as being down.
Bring this GRE interface up to send keepalives
This specifies whether or not the GRE keepalive packets will activate the tunnel. If set to YES
and the tunnel drops the GRE keepalive packet will try to raise the tunnel again. If set to NO
Digi TransPort User Guide 99