Content










8.1

Dial Backup
 


 
8.1.1


Configuring dial backup
 







A networking professional may determine
that certain mission-critical applications require additional WAN
links in order to prevent downtime. Multiple T1s may be provisioned
for a particular application and even backed up by a Frame Relay PVC.
Although the additional lines may have been leased for backup
purposes, these lines can also be used for load balancing or to route
certain traffic. Strictly speaking, such links are extra links, not
backup links.From the point of view of the Cisco IOS,
backup links are dialup technologies. A backup interface is an
interface that stays shut down until the primary link reaches an
administratively defined load.
The primary link is typically a Frame
Relay PVC, or a leased line.
Backup interfaces can be a physical
interface or a logical interface such as a dialer profile. Typical
backup interfaces include Integrated Services Digital Network Basic
rate Interface (ISDN BRI) and asynchronous interfaces. Serial
interfaces connected to either an asynchronous modem or ISDN BRI can
also be backup interfaces. The backup interface is also called the
secondary link.

To configure a backup interface in case
a primary line goes down, perform the following steps on one side of
the connection only:



Select the primary interface, and configure it for the
desired Layer 3 protocol, DDR, and encapsulation type. The
following steps demonstrate only the commands to enable a backup
interface:
Router(config)#interface
interface-type slot/port


Use the following command on the primary interface to specify the
interface or dialer interface to use for backup:
Router(config-if)#backup
interface interface-type slot/port
or
Router(config-if)#backup
interface dialer number


Define the period of time to wait before enabling the backup link after
the primary link goes down with the following command syntax:

Router(config-if)#backup
delay {enable-delay | never} {disable-delay
| never}




















 



Web Links

Evaluating Backup Interfaces, Floating Static Routes, and
Dialer Watch for DDR Backup



http://www.cisco.com/warp/public/123/ backup-main.html