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Understanding OSPF Configurations

To activate OSPF on a network, you must enable the protocol on all interfaces within the network on which OSPF traffic is to travel. To enable OSPF, you must configure one or more interfaces on the device within an OSPF area. Once the interfaces are configured, OSPF link-state advertisements (LSAs) are transmitted on all OSPF-enabled interfaces, and the network topology is shared throughout the network.

To complete the minimum device configuration for a node in an OSPF network involves:

  1. Configuring the device interfaces. See the Junos OS Network Interfaces Library for Routing Devices or the Junos OS Interfaces Configuration Guide for Security Devices.

  2. Configuring the router identifiers for the devices in your OSPF network

  3. Creating the backbone area (area 0) for your OSPF network and adding the appropriate interfaces to the area


    Once you complete this step, OSPF begins sending LSAs. No additional configuration is required to enable OSPF traffic on the network.

You can further define your OSPF network depending on your network requirements. Some optional configurations involve:

  • Adding additional areas to your network and configure area border routers (ABRs)

  • Enabling dial-on-demand routing backup on the OSPF-enabled interface to configure OSPF across a demand circuit such as an ISDN link. (You must have already configured an ISDN interface.) Because demand circuits do not pass all traffic required to maintain an OSPF adjacency (hello packets, for example), you configure dial-on-demand routing so individual nodes in an OSPF network can maintain adjacencies despite the lack of LSA exchanges.

  • Reducing the amount of memory that the nodes use to maintain the topology database by configuring stub and not-so-stubby areas

  • Ensuring that only trusted routing devices participate in the autonomous systems’ routing by enabling authentication

  • Controlling the flow of traffic across the network by configuring path metrics and route selection

When describing how to configure OSPF, the following terms are used as follows:

  • OSPF refers to both OSPF version 2 (OSPFv2) and OSPF version 3 (OSPFv3)

  • OSPFv2 refers to OSPF version 2

  • OSPFv3 refers to OSPF version 3