Dial Configuration Guide, Cisco IOS Release 15.5M&T

How VRF Aware Dialer Watch Works

The Cisco IOS Dialer Watch software feature integrates dial backup with routing capabilities. The Dialer Watch dial backup technology uses a route called watched-route, and whenever the watched-route entry is lost from a routing table, a new a backup link is brought up.

With the VRF Aware Dialer Watch feature introduced in Cisco IOS Release 12.3(7)T, you configure the watched-route as an IP address and VRF pair. A VRF is a per-Virtual Private Network (VPN) routing information repository that defines the VPN membership of a customer site attached to a network access server. A VRF consists of an IP routing table, a derived Cisco Express Forwarding (CEF) table, a set of interfaces that use the forwarding table, and a set of rules and routing protocol parameters that control the information that is included in the routing table. A separate set of routing and CEF tables is maintained for each VPN customer.

The corresponding VRF table configured in the VRF Aware Dialer Watch feature is used to detect when watched-route for the VRF has gone down. The original Dialer Watch feature looked only at the global routing table to determine if the watched route had gone down. The VRF Aware Dialer Watch feature allows configuring multiple VRFs apart from the global routing table. A secondary link will be brought up when the watched route in the corresponding VRF table goes down.

It is important to note that the VRF might have overlapping address space, as follows: At the provider edge (PE) router, each customer edge (CE) router—the router that is part of the customer network and that interfaces to a PE router—will have a corresponding VRF associated with it. Further, two CE routers might be using the same address space, so that the corresponding VRFs at the PE router will have overlapping address space. For this reason, you must configure the watched route as an IP address and VRF name pair, where the IP address is the watched IP address and the VRF name is the routing and forwarding instance to which the IP address belongs. Configuring the Dialer Watch feature with only the IP address did not ensure that the correct CE route would be dialed when a watched route went down. Configuring the new VRF Aware Dialer Watch feature with an IP address and VRF name pair ensures that the VRF table corresponding to the routing and forwarding instance to which the IP address belongs is found and the correct CE is dialed.

VRF Aware Dialer Watch Typical Scenario

Figure 1 shows a typical configuration that uses the VRF Aware Dialer Watch feature.

Figure 1 VRF Aware Dialer Watch Typical Configuration

A typical scenario for the VRF Aware Dialer Watch feature follows:

• A VRF router learns the route to the CE from a PE.
• The VRF router watches these learned routes to the CEs.
• The primary link between a PE and CE goes down.
• The watched route goes down in the VRF router.
• Dialer Watch call is initiated to the corresponding CE.

The backup link will be bound to the correct VRF. In configurations with a dialer profile, the dialer profile interface is statically bound to the corresponding VRF. In configurations without a dialer profile, a virtual access interface is created dynamically that is bound to the VRF.

Configuring the Dialer Watch List

This task configures a watched route made up of an IP address and VRF pair to be monitored by Dialer Watch using the dialer watch-list command. Most configurations contain several dialer watch-list commands, to specify a list of watched routes.

You must also configure a group number in a dialer watch-group interface configuration command, and the standard commands required to enable the router to perform dial-on-demand routing in addition to the Dialer Watch commands. Refer to Cisco IOS configuration guides and command references listed in the “Related Documents” section for additional information. See the “Configuration Examples for VRF Aware Dialer Watch” section for examples of how the VRF Aware Dialer Watch feature can be configured.

SUMMARY STEPS

1. enable

2. configure terminal

3. dialer watch-list group-number { ip ip-address address-mask [ vrf vrf-name ] | delay route-check initial seconds }

4. exit

DETAILED STEPS

VRF Aware Dialer Watch on a Legacy Dialer Configuration: Example

The following example specifies a pair of watched routes in a legacy dialer configuration. In this configuration, watch lists 1 and 2 are both watching the same IP address, but belong to different VRFs.

VRF Aware Dialer Watch on a Dialer Rotary Group: Example

The following example specifies a pair of watched routes in a dialer rotary group configuration. In this configuration, watch lists 1 and 2 are both watching the same IP address, but belong to different VRFs.

VRF Aware Dialer Watch on a Dialer Profile Configuration: Example

The following example specifies a pair of watched routes in a dialer profile configuration. In this configuration, watch lists 1 and 2 are both watching the same IP address, but belong to different VRFs.

Related Documents

Standards

MIBs

RFCs

Technical Assistance

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