LANCOM Reference Manual LCOS 3.50 Chapter 14: Virtual Private Networks—VPN
304
Virtual Private Networks—
VPN
translation via dynamic DNS services, a solution often used with flatrate
connections.
The described connection set up requires an ISDN connection for both
VPN gateways. But usually no charges will arise for this procedure.
Dynamic – dynamic
With LANCOM Dynamic VPN, VPN tunnels can also be set up between two
gateways that both only have dynamic IP addresses. Let's modify the previous
example so that in this case Gateway 1 also has a dynamic IP address. Once
again, Computer A would like to connect to Computer B:
햲Gateway 1 connects to its ISP and is assigned a public, dynamic IP
address.
햳It then calls Gateway 2 via ISDN to send this dynamic address. Three
procedures are used to send the address:
As information in the LLC element of the D-channel. In the D-
channel protocol of Euro-ISDN (DSS-1), the so-called LLC (Lower
Layer Compatibility) element can be used to send additional
information to the remote station. This transfer takes place before the
B-channel connection is established. Once the address has been sent
successfully, the remote station rejects the call. Charges are thus not
incurred for a B-channel connection. The IP address is sent
nevertheless for free in this case.
The LLC element is generally available as a standard feature in Euro-
ISDN that does not require registration or activation. It may be
disabled by telephone companies or individual exchanges, however.
Internet
Gateway 1
with dynamic IP
address
Computer BComputer A
Gateway 2
with dynamic
IP address
햲햴
햵
LAN 1 LAN 2
햳
Call via ISDN
ISDN