Understanding Dialer Interfaces

A dialer interface (dln) is a logical interface for configuring dialing properties and the control interface for a backup ISDN connection. You can configure multiple dialer interfaces for different functions on the device. The dialer interface can perform as a backup interface for one primary interface, as a dialer filter, or as a dialer watch interface, but these operations are mutually exclusive.

To enable dialer interfaces to work properly, you must configure the interface properties:

• Encapsulation mode—The interface can be configured in the following modes:

  • Multilink mode using Multilink Point-to-Point Protocol (MLPPP) encapsulation—MLPPP is a protocol for aggregating multiple constituent links into one larger PPP bundle. You can bundle up to eight B-channels.
  • Normal mode using Point-to-Point Protocol (PPP) encapsulation—PPP is for communication between two computers using a serial interface. Use this mode when the device is using only one B-channel.
  • Normal mode using Cisco High-Level Data Link Control (HDLC) encapsulation—Cisco-compatible DDLC is a group of protocols for transmitting data between network points. Use this mode when the device is using only one B-channel.

  Note: MPLS over ISDN is supported only with MLPPP encapsulation. If you use PPP or Cisco-HDLC, MPLS packets might be dropped.

• Logical unit—You can set the logical unit to 0 only, unless you are configuring the dialer interface for Multilink PPP encapsulation.
• Hold-time value—The hold-time value is used to damp interface transitions. When an interface goes from up to down, it is not advertised as down to the rest of the system until it remains unavailable for the hold-time period. Similarly, an interface is not advertised as up until it remains operational for the hold-time period. The hold time is three times the interval at which keepalive messages are sent.

• Delay intervals—You can configure the following delay intervals:

  • Activation delay—Time to wait before activating the backup interface once the primary interface is down. Default value is 0 seconds with a maximum value of 60 seconds. Use only for dialer backup and dialer watch.
  • Deactivation delay—Time to wait before deactivating the backup interface once the primary interface is up. Default value is 0 seconds with a maximum value of 60 seconds. Use only for dialer backup and dialer watch.
  • Redial delay—Number of seconds to wait before redialing a failed outgoing ISDN call. Default value is 3 seconds with a range from 2 to 255.
• Idle timeout—Time a connection is idle before disconnecting. Default value is 120 seconds with a range from 0 to 4,294,967,295. This option is used only to configure a dialer filter.
• Initial route check—Time to wait before checking if the primary interface is up. Default value is 120 seconds with a range of 1 to 300 seconds. This option is used only to configure dialer watch.
• Pool—Name of a group of ISDN interfaces configured to use the dialer interface.

Note: If you configure multiple dialer interfaces, ensure that the same IP subnet address is not configured on different dialer interfaces. Configuring the same IP subnet address on multiple dialer interfaces can result in inconsistency in the route and packet loss. The device might route packets through another dialer interface with the IP subnet address instead of through the dialer interface to which the ISDN modem call is mapped.

Related Topics

• Junos OS Feature Support Reference for SRX Series and J Series Devices