OSPF Network Design Solutions, Second Edition

Speaking OSPF

OSPF routers communicate with each other by using the various subprotocols with the OSPF protocol. OSPF runs on top of IP, although OSPF is composed of the following subprotocols:

• Hello

• Exchange

• Flooding

The following sections discuss these subprotocols in detail.

Types of OSPF Packets

OSPF uses five different packets in its protocols. Table 3-2 describes the different OSPF packet types. This section discusses each protocol and the role that the packets play.

Table 3-2. Overview of OSPF Packet Types

Packet Name	Type/Number	Function
Hello	1	Discovers and maintains neighbors.
Database description	2	Summarizes database contents.
Link state request	3	Requests LSAs that need to be downloaded to requesting router. Only sent during Exchange, Loading, ...