Cisco CISCO851-K9 - 851 Integrated Services Router - Backup Interfaces; Configuring Backup Interfaces; Floating Static Routes

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Cisco 850 Series and Cisco 870 Series Access Routers Software Configuration Guide
OL-5332-01
Chapter 13 Configuring Dial Backup and Remote Management
Dial Backup Feature Activation Methods
Backup Interfaces
When the router receives an indication that the primary line is down, a backup interface is brought up.
You can configure the backup interface to go down once the primary connection has been restored for a
specified period.
This is accomplished using dial-on-demand routing (DDR). When this is configured, a backup call is
triggered by specified traffic.
Note Even if the backup interface comes out of standby mode (is brought up), the router does not trigger the
backup call unless it receives the specified traffic for that backup interface.
Configuring Backup Interfaces
Perform these steps to configure your router with a backup interface, beginning in global configuration
mode:
Command Purpose
Step 1
interface type number
Example:
Router(config)# interface atm 0
Router(config-if)#
Enters interface configuration mode for the
interface for which you want to configure backup.
This can be a serial interface, ISDN interface, or
asynchronous interface.
The example shows the configuration of a backup
interface for an ATM WAN connection.
Step 2
backup interface interface-type
interface-number
Example:
Router(config-if)# backup interface bri 0
Router(config-if)#
Assigns an interface as the secondary, or backup
interface.
This can be a serial interface or asynchronous
interface. For example, a serial 1 interface could
be configured to back up a serial 0 interface.
The example shows a Basic Rate Interface
configured as the backup interface for the ATM 0
interface.
Step 3
exit
Example:
Router(config-if)# exit
Router(config)#
Enters global configuration mode.
Floating Static Routes
Floating static routes provide alternative routes for traffic. Floating static routes are not activated unless
a DDR backup call has been triggered by specified traffic for a backup interface.
Floating static routes are independent of line protocol status. This is an important consideration for
Frame Relay circuits because the line protocol may not go down if the data-link connection identifier
(DLCI) is inactive. Floating static routes are also encapsulation independent.