Specifications

Chapter 4. Configuring Special Features 103
Dial Backup
The Dial Backup capability provides a backup V.90 connection to the Internet when the default DSL link goes
down. The V.90 connection is provided through the console port. In this case, the console port is used as a serial
port and must be connected to an external V.90 modem.
Dial Backup is intended for customers with critical applications for which continuous Internet access is vital. If
the DSL link for those applications goes down, the router can automatically switch their traffic to the V.90
modem. Later, after determining that the DSL link is, once again, up and stable, the router automatically switches
the V.90 traffic back to the DSL link.
This feature may also be useful for a customer whose DSL line is not yet installed. The router can begin providing
service through a V.90 modem and later automatically switch to the DSL link when it becomes available.
Dial Backup with a Tunnel
You may wish to use an L2TP tunnel or IPSec tunnel only with the primary interface or only with the backup
interface.
If you do not want tunnel traffic to go through the backup V.90 modem, you should restrict the tunnel to use only
the primary interface. With this restriction in place, if the primary interface fails, the tunnel is terminated, and it is
not re-established with the backup interface.
Or, you might want a tunnel to be established only when the V.90 modem is being used. In this case, you would
restrict the tunnel to the backup interface only.
To set either restriction for an L2TP tunnel, use the command l2tp set wanif (page 328). On the command, you
specify the remote name that the tunnel is restricted to and the tunnel name. To restrict the tunnel to the backup
interface, specify the remote name that you created for the dialup parameters as described in Specifying the
Dialup Parameters, page 106.
To set a restriction for an IPSec tunnel, use the command ike ipsec set interface (page 337). The interface that
you specify on the command is the remote interface that the tunnel is to be restricted to. To restrict the tunnel to
the backup interface, specify the remote name that you created for the dialup parameters as described in
Specifying the Dialup Parameters, page 106.
Configuring Dial Backup
To set up the router to use the Dial Backup feature, you must:
¥ Connect a V.90 modem to the console port of the router.
¥ Configure the router software to use the Dial Backup feature.
To configure the Dial Backup option, you enter commands to:
¥ Enable the Dial Backup option.
¥ Set the conditions that determine the status of the DSL link.
¥ Minimum stability period for the DSL link status signal
¥ Optional IP addresses to be pinged and their ping interval, number of samples, and minimum success rate