Basics of OSPF

OSPF (Open Shortest Path First)

This is an open standard routing protocol. It finds a best route (own shortest path) from source to destination address (Router to Router).

• This is a link state protocol and similar to RIP (Distance Vector Protocol).
• It can be considered as one of the IGP (Interior Gateway Protocol) protocol.
• It uses multi cast address for normal communications.
• It Supports both IPV4 and IPV6.
• It can be run on most routers.
• It can link up with network in few seconds and can provide loop free paths.
• It have full support for sub nets and is easily scalable.
• This is basically used for largest size of network.
•  Industry standard use.

OSPF offers a feature named "Routing Area" which means dividing routers and communicating between them. 

Routers used, called as per areas are:

• Internal Router
• Backbone Router
• Area Border Router
• Autonomous System Boundary Router (ASBR)
• Designated Router
• Back up Designated Router

Messages used by OSPF

Hello Message

Database Description

Link State Request (LSR)

Link State Update (LSU)

Link State Acknowledgement (LSA)

OSPF routers generate this above messages and exchanges with neighboring routers. 

OSPF creates three tables in the router, Neighbor table, database table and routing table.

-DR