An ISDN interface module can be configured as the primary WAN connection for the Passport 4400, or it can be configured as a backup connection which becomes active only when the primary link fails. The Passport 4400 can also support two ISDN interface modules, one for the primary and one for the backup port. For information on how to configure primary and backup WAN ports, see Managing Primary and Backup Ports. ISDN over leased line is also supported to provide additional connection options.
This section discusses the following topics:
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