OSPF DEMAND CIRCUIT

OSPF DEMAND CIRCUIT

• IOS software release 11.2 ( RFC 1793)
• This function maintain neighbor relationships and ensure that the link-state databases are accurate and use far less bandwidth 
• OSPF Hellos and refresh of OSPF routing routing are suppressed on demand circuits
• This feature allows low-speed internet services such as analog dial and ISDN, to run OSPF without the need of periodic hellos and LSA flooding
• When a demand circuit is established a unique option bit (the DC bit) is exchanged between neighboring routers. If two routers negotiate the DC bit successfully they make a note of it and set a specific bit in LSA Age called the DoNotAge(DN).
• This feature is enabled with the interface-level-command "ip ospf demand-circuit

How is OSPF Demand Circuit and Normal Circuit?

• Two features of OSPF over demand circuit makes different from a normal circuit
• Suppressed periodic hellos
• Suppressed periodic LSA refresh 
• In the demand circuit, the periodic LSA refresh occurs 
• if change in network topology
• if a router in the OSPF domain that can not understand demand circuits

 CONFIGURATION
Router (config) # interface xxx
Router (config-if) # ip ospf demand-circuit

Network Design

Configuration

Verification

Reference

Cisco OSPF Demand Circuit Configuration Guide
INE Lab Work Book - OSPF Demand Circuit