ABSTRACT
This chapter introduces the control packets of OSPF and IS-IS, and discusses the Hello protocol and the designated router election. It explains how routing information is disseminated, and how it is updated. The chapter examines the initial Link State Database (LSDB) synchronization process. It describes when routing information must be originated and deleted. The LSDB must be kept updated and synchronized across all routers of a routing domain. There are three synchronization mechanisms: the Hello protocol, the flooding procedure, and initial LSDB synchronization process. In both OSPF and IS-IS, routers establish and maintain neighborhood relationships at specific interfaces using the Hello protocol. This protocol allows learning that a neighbor exits and is alive and determining the kind of relationship that can be established with the neighbor. One of the roles of the Hello protocol is to determine if two neighbors can become adjacent.
