- Enterasys Security Router User's Guide

Overview of Dial Backup
XSR User’s Guide 10-13
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 10-41 for an example.
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.
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.