Configure OSPF on the On-Demand Circuit

The OSPF on-demand circuit is an extension of the OSPF protocol and allows operations on the On-demand circuit, just like the Integrated Service Digital Network (ISDN), X.25 switched virtual circuit (SVC), and dial-up line. This feature supports RFC1793 and extended OSPF supports request circuits.
Previously, OSPF periodic hello packet and link status advertisement (LSA) Updates exchange between routers connected to the request circuit, even if the hello packet and link status advertisement (LSA) the information in the update has not changed.
After this feature is enabled, periodic hello packets are prohibited, and the link status advertisement (LSA) Periodically refreshes information and will not be published to the request circuit. The link is proposed only when the packet is first exchanged or the information is changed. When the network topology is stable, the following data link layer can be disabled.
When connecting a remote switch or Telecom branch to the OSPF trunk of the central site, this feature is used actively. In this case, the OSPF request circuit can benefit from the OSPF of the entire domain with minimum connection overhead. When there is no "real" data to be transmitted, the request circuit is not activated, so that the fee for periodic refresh of hello packet, link status advertisement (LSA) and other protocol update information is reduced.
The preceding protocols, such as hello and link status advertisement (LSA), are transmitted on an on-demand circuit only when the first setup and topology changes. This means that in order to maintain the integrity of the network topology, important changes of the topology must be reflected according to the shortest path priority algorithm, and the change information must be transmitted. However, periodic refreshes that do not contain changed information are not transmitted through links.
To configure the OSPF on-demand circuit and start global mode, run the following command:

Procedure	Command	Function
Step 1	Router ospf process-id	Make the OSPF operation effective.
Step 2	Interface type number	Enter the interface configuration method.
Step 3	Ip ospf demand-circuit	Configure OSPF for the on-demand circuit.

If the router is an integral part of the point-to-point topology, you only need to use this command to configure one end of the Request circuit. However, all routers must load this feature. If the router is an integral part of a one-to-multiple interface topology, you only need to use this command to configure the Multi-Point End of the Request circuit.
Considerations for implementation

Before performing this feature, consider the following factors:

Because the link status advertisement (LSA) that includes topology changes will be published to the on-demand circuit, it is best to put the request circuit into the OSPF stub area or non-pure Stub area (NSSA, isolate the request circuit from as many topology changes as possible.
In the stub area or non-pure Stub area (NSSA), each vro in the zone must be loaded with this feature using the on-demand circuit function. If this feature is configured in one common area, all other common areas must support this feature for the request circuit function to take effect. This is because the LSA will be released throughout the region.
This attribute cannot be executed in the broadcast network topology because the preceding protocols (such as hello packet and link status announcement LSA) cannot be effectively disabled in this structure, that is, the link remains active.