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Backup Connection Using the Untrusted Ethernet Port in ScreenOS Devices


When using ADSL, the adsl1 interface serves as the primary connection to the Internet. However, you can configure a backup connection to the Internet using the Untrusted Ethernet port or the Modem port on the security device.


You can configure only one backup interface.

To configure the backup interface, bind both the adsl1 and backup interface to the Untrust zone to automatically configure the interface failover. If the ADSL interface becomes unavailable, the security device automatically sends outgoing traffic to the backup interface, which connects to the ISP account. When the ADSL interface is again available, the device automatically sends outgoing traffic to the adsl1 interface.

To configure the serial interface for the modem, you must have the following information:

  • Login and password for the account to the dialup service provider


    All passwords handled by NSM are case-sensitive.

  • Primary phone connection for dialing into the account

  • Modem initialization string

For more information about configuring the serial interface on a security device, see the “ Interface Redundancy” chapter in the “ High Availability” volume of the Concepts & Examples ScreenOS Reference Guide.

For details on configuring the modem and ISP settings for the serial interface in NSM, see Example: Configuring Modem Connections (NSM Procedure) .