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Example: Configuring OSPF Demand Circuits

Requirements

Before you begin:

• Configure the device interfaces. See the Junos® OS Network Interfaces.

  Note: If you are using OSPF demand circuits over an ISDN link, you must configure an ISDN interface and enable dial-on-demand routing. See the Junos® OS Network Interfaces.

• Configure the router identifiers for the devices in your OSPF network. See Example: Configuring an OSPF Router Identifier.
• Configure a single-area OSPF network. See Example: Configuring a Single-Area OSPF Network.
• Configure a multiarea OSPF network. See Example: Configuring a Multiarea OSPF Network.

Overview

OSPF sends periodic hello packets to establish and maintain neighbor adjacencies and uses link-state advertisements (LSAs) to make routing calculations and decisions. OSPF support for demand circuits is defined in RFC 1793, Extending OSPF to Support Demand Circuits, and suppresses the periodic hello packets and LSAs. A demand circuit is a connection on which you can limit traffic based on user agreements. The demand circuit can limit bandwidth or access time based on agreements between the provider and user.

You configure demand circuits on an OSPF interface. When the interface becomes a demand circuit, all hello packets and LSAs are suppressed as soon as OSPF synchronization is achieved. LSAs have a DoNotAge bit that stops the LSA from aging and prevents periodic updates from being sent. Hello packets and LSAs are sent and received on a demand-circuit interface only when there is a change in the network topology. This reduces the amount of traffic through the OSPF interface.

• Periodic hellos are only suppressed on point-to-point and point-to-multipoint interfaces. If you configure demand circuits on an OSPF broadcast network or on an OSPF nonbroadcast multiaccess (NBMA) network, periodic hello packets are still sent.
• Demand circuit support on an OSPF point-to-multipoint interface resembles that for point-to-point interfaces. If you configure a point-to-multipoint interface as a demand circuit, the device negotiates hello suppression separately on each interface that is part of the point-to-multipoint network.

This example assumes that you have a point-to-point connection between two devices using SONET/SDH interfaces. A demand-circuit interface automatically negotiates the demand-circuit connection with its OSPF neighbor. If the neighbor does not support demand circuits, then no demand circuit connection is established.

In this example, you configure OSPF interface so-0/1/0 in OSPF area 0.0.0.1 as a demand circuit.

Configuration

CLI Quick Configuration

To quickly configure an OSPF demand circuit interface, copy the following command and paste it into the CLI. You must configure both neighboring interfaces for OSPF demand circuits for the connection to be established.

Step-by-Step Procedure

1. Create an OSPF area.

   Note: For OSPFv3, include the ospf3 statement at the [edit protocols] hierarchy level.

   [edit ]user@host# edit protocols ospf area 0.0.0.1
2. Configure the neighboring interface as a demand circuit.
   [edit protocols ospf area 0.0.0.1]user@host# set interface so-0/1/0 demand-circuit
3. If you are done configuring the device, commit the configuration.
   [edit protocols ospf area 0.0.0.1]user@host# commit

   Note: Repeat this entire configuration on the other neighboring interface.

Results

Confirm your configuration by entering the show protocols ospf command. If the output does not display the intended configuration, repeat the instructions in this example to correct the configuration.

To confirm your OSPFv3 configuration, enter the show protocols ospf3 command.

Verification

Confirm that the configuration is working properly.

Verifying the Status of Neighboring Interfaces

Purpose

Verify information about the neighboring interface. When the neighbor is configured for demand circuits, a DC flag displays.

Action

From operational mode, enter the show ospf neighbor detail command for OSPFv2, and enter the show ospf3 neighbor detail command for OSPFv3.