Digi TransPort WR11 User Manual page 519

Configuring Virtual Private Networking (VPN)
L2TP Window Size
The L2TP window size is selected from this drop down list. Available values are from 1 to 7.
Route UDP packets over interface x,y
These two text boxes specify the interface and its instance number for L2TP UDP sockets.
Specifying these parameters allow the router to raise the interface should it be disconnected.
Source Port Normal/Variable
These radio buttons select the source port for the L2TP tunnel. Setting this setting to Normal
uses the default port number, 1701. If set to Variable, this setting uses a random source port
value.
Name
The name that identifies the router during the negotiation phase when establishing an L2TP
tunnel.
Authentication Off/Secret
The radio buttons select whether or not to use authentication. This is normally set to Off as
most host systems require using IPsec over L2TP tunnels. If Authentication is set to On,
authentication is enabled and the Secret parameter becomes relevant. The value in the text
box contains a passphrase shared with the host. The router uses this passphrase if the remote
host requests authentication and Authentication is set to Off here.
3. Configure the advanced L2TP parameters as needed:
Retransmit interval s milliseconds
The amount of time, in milliseconds, the router waits before retransmitting a Start Control
Connection Request (SCCRQ) frame. The default value of 250ms should be changed to a
higher value (say 4000ms) if L2TP is running over a GPRS link.
Retransmit count n
When using L2TP over GPRS or satellite networks, the first few packets are sometimes lost.
Setting the retransmit count in the text box to a higher value than the default of 5 will increase
reliability of the tunnel.
Layer 1 Interface Sync port n/ISDN
These radio buttons select the layer 1 (physical) interface to use to terminate the L2TP
connection. The available options are ISDN or one of the router's synchronous serial ports.
When Sync port n is selected, the sync port number is selected from the drop-down list.
Allow this L2TP tunnel to answer incoming ISDN calls
When enabled, the L2TP entity answers incoming ISDN calls.
MSN
The filter for the ISDN Multiple Subscriber Numbering (MSN). It is blank by default but when the
answering facility (above) is enabled, the router only answers ISDN calls where the trailing
digits match this MSN value. For example, setting the MSN value to 123 prevents the router
from answering calls from any calling number that does not end in 123. Not applicable when
answering is off.
Digi TransPort® Routers User Guide
Configure Internet Protocol security (IPsec)
519