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The TCP/IP Guide  9  TCP/IP Lower-Layer (Interface, Internet and Transport) Protocols (OSI Layers 2, 3 and 4)       9  TCP/IP Internet Layer (OSI Network Layer) Protocols            9  TCP/IP Routing Protocols (Gateway Protocols)                 9  TCP/IP Interior Routing Protocols (RIP, OSPF, GGP, HELLO, IGRP, EIGRP)                      9  Open Shortest Path First (OSPF)

OSPF Overview, History, Standards and Versions 1 2 3 OSPF Hierarchical Topology, Areas and Router Roles

LSDB Information Storage and Propagation

An important point to remember about the LSDB is that even though each router maintains it, the database isn't constructed from the perspective of the individual router. A router's LSDB represents the topology of the entire AS, including links between routers that may be rather distant from it. So, for example, RA would keep the entire database in its storage area, including information about RC and RD, to which it does not connect directly.

Since in basic topology all the routers are peers and maintain information for the entire AS, they in theory should have the exact same LSDB contents. When a router is first turned on it may in fact have different LSDB information than its neighbors, but this will be corrected through the exchange of update messages containing link-state advertisements (LSAs). Eventually all routers should converge to the same information. We will see how this works in the topic on OSPF messaging.

OSPF, as an interior routing protocol, is of course used only within the autonomous system. In most cases the AS will be connected to other ASes through one or more of its routers. The routers that connect the AS to other ASes are often called boundary routers. These devices will use OSPF to communicate within the AS, and an exterior routing protocol (typically BGP) to talk to routers outside the AS. The name boundary router refers to the fact that these devices are usually located on the periphery of the AS.

OSPF Overview, History, Standards and Versions 1 2 3 OSPF Hierarchical Topology, Areas and Router Roles