Enterasys Networks X-PeditionTM manual Overview of Dial Backup, Sequence of Backup Events

Overview of Dial Backup

XSR(config-if<D1>)#dialer idle-timer 0

XSR(config-if<D1>)#dialer map ip 10.10.10.2 9053617921

XSR(config-if<D1>)#dialer map ip 10.10.10.3 9053617363

XSR(config-if<D1>)#encapsulation ppp

XSR(config-if<D1>)#ip address 10.10.10.1 255.255.255.0

XSR(config-if<D1>)#no shutdown

Overview of Dial Backup

The dialed backup feature provides a backup link over a dial line. The backup link is brought up when failure occurs in a primary link, and is brought down when the primary link is restored.

Dial Backup Features

•User controllable delay when the link is activated for backup, and when the link is deactivated, that is, brought down.

•Dial backup is triggered when the XSR detects a primary IP circuit failure and backup is triggered to end when the circuit comes up. The secondary line is generated when an entry in routing table is lost.

•PPP and Frame Relay encapsulation. For Frame-Relay encapsulation the Dialer interface must be associated with a dialer sub-interface which is configured with a Frame Relay DLCI and IP address, while the parent Dialer interface carries the encapsulation information and call parameters (dial pool, dial string, and dial class). Refer to “Configuration for Frame Relay Encapsulation” on page 10-41for an example.

Note: Dial backup may not be activated if the XSR's link at local site is up and a remote site’s link is down.

Keep in mind the following when configuring backup:

•Use backup on primary interfaces that have an IP address configured only; that is, the backup command must be entered at the configuration level where an IP address is specified. For example, if you configure a Serial interface and sub-interface, be sure to specify backup at the sub-interface configuration mode, not at Serial interface mode.

Sequence of Backup Events

The following sequence of events occurs when a primary link fails and a backup line fails:

1.A Primary Link fails.

2.A link failure is detected. This link is configured for backup, and is monitored.

3.The Backup function is notified about link failure.

4.With the interface down, all routes reachable through that interface are removed from the routing table.

5.Backup function invokes the dialer to activate the configured (dial) backup interface. Activating the backup link can be delayed, if configured as such.

6.Backup link is up.

7.Backup link is activated.

XSR User’s Guide 10-13