OSPF Messages

1. Hello
        * Is used to discover neighbors
        * Bring a neighbor relationship to a 2-way state.
        * Is used to keep neighborship up between two routers
        * To bring neighborship up, both devices must agree on some parameters

2. DBD
        * Is used to exchange the LSA header during the initial topology exchange so that router knows a list of LSAs the neighbor contains
        * Is also used to perform the master and slave election
        * Master/Slave election happens to check the reliability between routers(in the future we will have a discussion about how Master/Slave election happens and the benefits)

3. LS-Request
        * Routers send Request to the neighbor router to get the full database
        * Routers use previously received DBD to send Request

4. LS-Update
        * This process happens in 3 different ways
                The router sends full updates in the response to previous received LS-Request for requested DBD while the initial neighborship process
                Whenever routers get a change they send a full update in the same area
                Routers exchange full updates after every 1800sec if there are no changes triggered

5. LS-Ack
        * Whenever routers send any update to neighbors they reply with Ack to let the router knows that they have received the update
        * Each LSA received must be explicitly acknowledged
        * Multiple LSAs can be acknowledged in a single LSAck packet.