OSPF

Link state protocols know whether a link is up or down and how fast it is and calculates a cost to 'get there'.

OSPF selects the best routes by finding the lowest cost paths to a destination. All router interfaces (links) are given a cost. The cost of a route is equal to the sum of all the costs configured on all the outbound links between the router and the destination network, plus the cost configured on the interface .

OSPF Router Types

• Internal Router
• Backbone Router
• Area Border Router (ABR)
• Autonomous System Boundary Router (ASBR)
• Designated Router (DR)
• Backup Designated Router (BDR

Virtual Links

Virtual links are used when you have a network that must be connected to an existing OSPF system, but cannot be physically connected directly to the routers in the OSPF backbone area. You can configure an OSPF virtual link from the area to a backbone router, creating a virtual direct connection to the backbone area.

Type- It specifies the type of OSPF packet. There are 5 different types of OSPF packets. (1-byte)

1- Hello packet
2- Database Descriptor packet
3- Link State Request packet

4- Link State Update packet
5- Link State Acknowledgment packet