Eicon Networks DIVA LAN ISDN - Manual (Page 88)

Chapter Six: Security Callback 88
Callback
Callback is another effective method to control access to the DIVA LAN ISDN Modem. When callback is
enabled, the DIVA LAN ISDN Modem functions as a callback client, and the remote site being called
functions as a callback server.
The client calls the server, the connection is dropped or disconnected, then waits for the server to call back to
re-establish the connection. While waiting for the server to call back, the DIVA LAN ISDN Modem may
accept incoming calls that are not from the server. To ensure that only calls from the server are accepted you
can use call authentication (set the always authenticate remote option as shown on page 87) to validate the
incoming call.
The DIVA LAN ISDN Modem can only function as a callback client.
Note When you enable callback using the web configuration interface, the DIVA LAN ISDN Modem
automatically enables support for incoming data calls (page 83).
Callback modes
Two callback modes are available. Each provides different features. For callback to work, both client and
server must use the same mode.
Callback control protocol
This is a Microsoft-developed solution. It is used by NT4, and devices from Cisco, Ascend, and other vendors.
NCP enables you to specify a time delay before the server calls back, and supports both the user specified and
administrator specified options.
ISDN callback
Unlike the callback control protocol, the server does not answer the initial call from the DIVA LAN ISDN
Modem when using ISDN callback mode. Therefore, there is no charge for the call. This can be advantageous
if you are making a lot of calls without a flat-rate package, or are making long distance calls.
ISDN modem only works with Cisco IOS. It uses caller ID information to return the call. Therefore, caller ID
must be enable on your line to use this mode.
Callback options
Two callback options are available: user specified and administrator specified.
User specified
This option requires that the DIVA LAN ISDN Modem supply the server with the callback number to use. If
the server is on a PBX, or must dial long distance, you may need to include appropriate dialing prefixes.
Contact the system administrator of the server to determine the exact requirements.
The main advantage of this option is that if you change the DIVA LAN ISDN Modem’s ISDN phone numbers,
you do not have to inform the server, since you supply the phone number with each call.
Administrator specified
With this option, the DIVA LAN ISDN Modem does not supply the server with a number to dial. Instead, the
remote identifies the DIVA LAN ISDN Modem by its caller ID or information supplied during call
authentication. The server then consults a pre-configured table to determine the number to dial.
The main advantage of this option is centralized security. The server maintains a list of all valid clients, with
their physical phone numbers and security information.
Note It may not always be possible to support an MLPPP connection with the administrator specified option.
The reason for this is that the server will only have one number configured for callback. When it tries to
establish the second channel, it gets a busy signal. The solution is to use user specified, and send the server the
two numbers that are required.