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Barracuda CloudGen Firewall

How to Configure an ISP with ISDN

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The Barracuda CloudGen Firewall supports up to four ISDN connections. The ISDN connection is initiated at startup or in Dial-On-Demand mode when used as a backup connection.


Before You Begin

  • Verify that you have the necessary configuration information provided to you by your ISP.
  • Before configuring channel bonding (=mppp), verify that your provider supports this feature.

Step 1. Create and Configure the ISDN Connection

Enter the properties for the ISDN modem card and configure connection details.

  1. Go to CONFIGURATION > Configuration Tree > Box > Network.
  2. In the left menu, select xDSL/DHCP/ISDN.
  3. Click Lock.
  4. Set ISDN Enabled to Yes.
  5. To use the ISDN modem as a backup connection, set Standby Mode to Yes.

    Standby connections must be started by a command line script. For more information, see Operating an ISDN Link in Standby Mode.

  6. Click Set next to ISDN Settings. The ISDN Settings window opens.
  7. Select your card type from the ISDN Modem Card list.
  8. Enter the Provider Phone Number that has been given to you by your provider.
  9. Select the applicable Encapsulation Mode. The following modes are available:
    • SyncPPP (default) – Bit-oriented transfer protocol.
    • RawIP – No PPP; IP addresses must be specified manually. This mode can only be used with static IP addresses.
  10. Select the Dial Mode. If set to Dial-On-Demand, specify Idle Hangup Time to automatically disable the link when it is not used anymore.
  11. Enable Use Channel Bonding if applicable and supported by your ISP:
    1. Click Set next to Channel Bonding Settings and adjust the on-demand bandwidth allocation for the second channel.
    2. Enable Use 2nd S0 Bus if a 2nd S0 is required.
    3. Click Set next to Parameters for 2nd S0 Bus and configure the settings.
  12. If you want to restrict the time when the ISDN connection can be established, set Dial Allowed From / Until.
  13. If your ISP assigned your connection a static address, disable Dynamic Address Assignment and enter the Static IP/Mask and Static Gateway IP address.

Step 2. Configure Authentication

Select an authentication method and enter the credentials provided by your ISP.

  1. In the Authentication section, select the Authentication Method that is used for the connection.
  2. Enter the User Access ID, Sub-ID, and Password assigned by your provider. Do not enter the # sign.
  3. If required, enter the Provider Name, which is appended to your User Access ID.
  4. Select Use ProviderDNS to use the DNS servers assigned by your provider.
  5. When using dynamic DNS, select Use Dynamic DNS and click Set. The Dynamic DNS Params window opens.
    1. Select a dynamic DNS Service Type. For information about available DynDNS service types, see
    2. Enter the Dyn DNS Name that was registered at
    3. Enter the User Access ID and Password for accessing the server as defined during registration at

Step 3. Configure Connection Monitoring

Configure connection monitoring by entering a list of health check targets that are only reachable through this connection. Should the ping to these health check targets fail, the Barracuda CloudGen Firewall will terminate and reestablish the connection until the monitoring target IP addresses are reachable again.

  1. In the Connection Monitoring section, select the Monitoring method:
    • LCP – If ping fails, the dial-in daemon is probed directly via LCP.
    • ICMP – The Barracuda CloudGen Firewall probes the Reachable IPs and, if there is no response, the gateway.
    • StrictLCP – No ICMP probing occurs.
  2. Enter one or more Reachable IPs to monitor the availability of the connection. The target IP addresses should only be accessible via this connection.
  3. Select the Unreachable Action to be taken if the connection cannot be established. The following options are available:
    • Restart – Restarts the connection.
    • Increase-Metric – Changes the preference for ISDN routes until the probe succeeds.
  4. Click OK.
  5. Click Send Changes and Activate.

Step 4. Activate Network Changes

You must activate the network changes to bring up the xDSL connection.

  1. Go to CONTROL > Box.
  2. In the left menu, expand the Network section and click Activate new network configuration.
  3. Select Failsafe. The 'Failsafe Activation Succeeded' message is displayed after your new network configurations have been successfully activated.

Your ISDN connection is now active and the IP addresses assigned by your ISP are visible on the CONTROL > Network page. The status icons next to the ISDN interface are green, indicating an active connection. If the ISDN connection is your primary uplink, the default route pointing to the ISDN interface is also created. If more than one default route is present, the connection with the lowest route metric is used.

Operating an ISDN Link in Standby Mode

Enable Standby Mode in the ISDN configuration if you want to use the ISDN connection as a backup uplink. In standby mode, activation and subsequent monitoring of the connection must be triggered externally. Standby mode also lets you combine HA setups for HA ISDN  connections.

  1. The ISDN routes are set to pending, and the Barracuda CloudGen Firewall does not check whether they are established.
  2. The configuration is completely run through but the connection is not yet established.

Standby connection can only be started by a command line script. Example usage:

  • connection start: /etc/phion/dynconf/network/isdnrestart &
  • connection stop: /etc/phion/dynconf/network/wipeisdn &