Dial Configuration Guide, Cisco IOS Release 15.5M&T

Dialer Watch Overview

Dialer Watch is a backup feature that integrates dial backup with routing capabilities. Prior dial backup implementations used the following conditions to trigger backup:

• Interesting packets were defined at central and remote routers using dial-on-demand routing (DDR).
• Connection loss occurred on a primary interface using a back up interface with floating static routes.
• Traffic thresholds were exceeded using a dialer load threshold.

Prior backup implementations may not have supplied optimum performance on some networks, such as those using Frame Relay multipoint subinterfaces or Frame Relay connections that do not support end-to-end permanent virtual circuit (PVC) status updates.

Dialer Watch provides reliable connectivity without relying solely on defining interesting traffic to trigger outgoing calls at the central router. Dialer Watch uses the convergence times and characteristics of dynamic routing protocols. Integrating backup and routing features enables Dialer Watch to monitor every deleted route. By configuring a set of watched routes that define the primary interface, you are able to monitor and track the status of the primary interface as watched routes are added and deleted. Monitoring the watched routes is done in the following sequence:

1. Whenever a watched route is deleted, Dialer Watch checks whether there is at least one valid route for any of the defined watched IP addresses.

2. If no valid route exists, the primary line is considered down and unusable.

3. If a valid route exists for at least one of the defined IP addresses and if the route is pointing to an interface other than the backup interface configured for Dialer Watch, the primary link is considered up.

4. If the primary link goes down, Dialer Watch is immediately notified by the routing protocol and the secondary link is brought up.

5. Once the secondary link is up, at the expiration of each idle timeout, the primary link is rechecked.

6. If the primary link remains down, the idle timer is indefinitely reset.

7. If the primary link is up, the secondary backup link is disconnected. Additionally, you can set a disable timer to create a delay for the secondary link to disconnect, after the primary link is reestablished.

Dialer Watch provides the following advantages:

• Routing—Backup initialization is linked to the dynamic routing protocol, rather than a specific interface or static route entry. Therefore, both primary and backup interfaces can be any interface type, and can be used across multiple interfaces and multiple routers. Dialer Watch also relies on convergence, which is sometimes preferred over traditional DDR links.
• Routing protocol independent—Static routes or dynamic routing protocols, such as Interior Gateway Routing Protocol (IGRP), Enhanced IGRP (EIGRP) or Open Shortest Path First (OSPF) can be used.
• Nonpacket semantics—Dialer Watch does not exclusively rely on interesting packets to trigger dialing. The link is automatically brought up when the primary line goes down without postponing dialing.
• Dial backup reliability—DDR redial functionality is extended to dial indefinitely in the event that secondary backup lines are not initiated. Typically, DDR redial attempts are affected by enable-timeouts and wait-for-carrier time values. Intermittent media difficulties or flapping interfaces can cause problems for traditional DDR links. However, Dialer Watch automatically reestablishes the secondary backup line on ISDN, synchronous, and asynchronous serial links.

The following prerequisites apply to Dialer Watch:

• The router is dial backup capable, meaning the router has a data communications equipment (DCE), terminal adapter, or network termination 1 device attached that supports V.25 bis.
• The router is configured for DDR. This configuration includes traditional commands such as dialer map and dialer in-band commands, and so on.
• Dialer Watch is only supported for IP at this time.

For information on how to configure traditional DDR for dial backup, see the other chapters in the “Dial Backup” part of this publication.

Note The Multilink PPP Minimum Links Mandatory feature has priority over the Dialer Watch feature. If both features are configured simultaneously then the ISDN link will not become inactive even if the primary link is active.

Configuring the Interface to Perform DDR Backup

Perform this task to configure the interface to perform DDR backup. This task initiates Dialer Watch.

SUMMARY STEPS

1. enable

2. configure terminal

3. interface type number

4. dialer watch-group group-number

DETAILED STEPS

Creating a Dialer List

Perform this task to create a dialer list. This task defines the IP addresses that you want to be watched.

SUMMARY STEPS

1. enable

2. configure terminal

3. dialer watch-list group-number ip ip-address address-mask

DETAILED STEPS

Setting the Disable Timer on the Backup Interface

Perform this task to set the disable timer on the backup interface. You may want to implement a delay before the backup interface is dropped once the primary interface recovers. This delay can ensure stability, especially for flapping interfaces or interfaces experiencing frequent route changes.

Note The dialer watch-disable command used in Dialer Watch configurations was replaced in Cisco IOS Release 12.3(11)T by the dialer watch-list delay command. When using the dialer watch-list delay command in software later than Cisco IOS Release 12.3(11)T, you can specify both a connect and disconnect timer for the disable timer. The disconnect time specifies that the disconnect timer is started when the secondary link is up and after the idle timeout period has expired, and only when software has determined that the primary route has come up.

In Cisco IOS Releases Prior to 12.3(11)T

Perform this task to apply a disable timer.

SUMMARY STEPS

1. enable

2. configure terminal

3. interface type number

4. dialer watch-disable seconds

DETAILED STEPS

In Cisco IOS Release 12.3(11)T and Later

Perform this task to apply a disable timer.

SUMMARY STEPS

1. enable

2. configure terminal

3. interface type number

4. dialer watch-list group-number delay { connect connect-time | disconnect disconnect-time }

DETAILED STEPS

Configuring Dialer Watch Prior to Cisco IOS Release 12.3(11)T: Example

In the following example, an ISDN BRI line is used to back up a serial leased line connection by configuring the Dialer Watch feature on a router named maui-soho-01. The Dialer Watch feature enables the router to monitor the existence of a specified route. If that route is not present, the backup interface is activated. Unlike other backup methods, the Dialer Watch feature does not require interesting traffic to activate the backup interface. The configuration shown in Figure 1 uses legacy dial-on-demand routing (DDR) and the Open Shortest Path First (OSPF) routing protocol. Dialer profiles can be used in place of DDR. Once the backup connection is activated, you must ensure that the routing table is updated to use the new backup route. Additional information about the Dialer Watch feature is available at the following website:

http://www.cisco.com/warp/public/129/bri-backup-map-watch.html

For additional information on configuring legacy DDR, dialer profiles, PPP, and traditional dial backup features, see the relevant chapters in this publication.

Figure 1 Dialer Watch for Frame Relay Interfaces

Note The following example uses commands supported in Cisco IOS software prior to Release 12.3(11)T. See the updated example for configuring Dialer Watch after Cisco IOS Release 12.3(11)T that follows this example.

Configuration for maui-soho-01

Configuration for maui-nas-05

Configuring Dialer Watch with Cisco IOS Release 12.3(11)T and Later Releases: Example

The following example shows how to configure Dialer Watch using the dialer watch-list delay command that replaced the dialer watch-disable command.

Configuration for maui-soho-01

Configuration for maui-nas-05

Related Documents

Standards

MIBs

RFCs

Technical Assistance

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