Open Shortest Path First (OSPF) - 9 : OSPF Packets

This playlist provides an overview of the Open Shortest Path First (OSPF) routing protocol and its advantages and disadvantages:

This diagram shows the basic format of the OSPF packet.
First there is the version number, which identifies the OSPF version used.

Next is the type field, which identifies the OSPF packet type. This field will either contain a hello message or a database description. Hello messages are used to establish and maintain neighbor relationships. The database description describes the contents of the router's topological database.

There are three types of messages that can reside in the database description type field:
- One is the link-state request, which is used to request pieces of the topological database from a neighbor router
- Or, the field might contain a link-state update, which is a response to a link-state request packet

- Or, finally, the link-state acknowledgment acknowledges the receipt of a link-state update packet

The next field is packet length, which specifies the size of the total packet.

Then, the router ID field identifies the source of the packet.

Next is area ID, which identifies the OSPF area to which the packet belongs.

Then we have the checksum, which checks the entire packet contents for any damage suffered in transit.

The authentication type field contains the authentication type. All OSPF protocol exchanges are authenticated. The authentication type is configurable.

Following that is the authentication field containing the authentication information.

And finally, the data field contains the information being exchanged.