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̈ Chapter 14: Virtual Private Networks—VPN LANCOM Reference Manual LCOS 3.50
305
Virtual Private Networks—
VPN
The LLC element is not available in 1TR6, the German national ISDN.
The procedure described above thus will not work with 1TR6.
୴ As a subaddress via the D-channel. If it is not possible to send the
address via the LLC element, Gateway 1 will attempt to send the
address as a so-called subaddress. Like the LLC element, the
subaddress is an information element of the D-channel protocol that
permits short items of information to be sent free of charge. In this
case, the telephone company must enable the 'subaddressing' feature
first; this is generally subject to a charge. As with the LLC element, the
call is rejected by the remote station once the IP address has been
transferred successfully. The connection thus remains free of charge.
୴ Via the B-channel. If both attempts to send the IP address via the
D-channel fail, then a conventional connection via the B-channel
must be established to send the IP address. The connection is dropped
immediately after the IP address has been sent. This connection is
subject to the usual charges.
ቤ Gateway 2 connects to the ISP and receives a dynamic IP address.
ብ Gateway 2 now sets up the VPN tunnel to Gateway 1.
Dynamic VPN works only between LANCOM that each feature at least
one ISDN port that can be used for the ISDN connection.
Dynamic IP addresses and DynDNS
It is also possible to establish a connection between two stations using
dynamic IP addresses by using so-called dynamic DNS services (DynDNS). The
address of the tunnel end-point is not defined as an IP number (which is, of
course, dynamic and subject to frequent change) but as a static name instead
(e.g. MyLANCOM@DynDNS.org).
Two things are needed for translating a name to its current IP address: A
dynamic DNS server and a dynamic DNS client:
̈ The first, available from numerous providers in the Internet, is a server
that is in communication with Internet DNS servers.
̈ The dynamic DNS client is integrated in the device. It can make contact to
any one of a number of dynamic-DNS service providers and, assuming
that a user account has been set up, automatically update its current IP