Link-State Routing Protocols
ink-state routing protocols are more advanced than distance-vector
protocols because, unlike distance-vector, they do not send periodic routing
updates. When a change in the network occurs, the routers send Link State
Advertisements (LSAs) about the change that has occurred. The whole rout-
ing table is not sent as in distance-vector; only the needed information is sent.
Each device that receives the LSA makes a copy, updates its topological
database, and forwards this LSA to all neighbors using multicast addressing.
This flooding of the LSA is to make sure that all devices know about the
change in the internetwork.
Hierarchical design of the physical network is critical in larger networks
to reduce the flooding needed, which reduces the convergence time of the
network. This topic will be covered in more detail in Chapters 4 and 5,
"Interconnecting OSPF Areas."
Table 2.3 compares the characteristics of the various link-state routing
protocols. Enhanced IGRP is called an advanced distance-vector protocol by
Cisco, but it has link-state features as well. Intermediate System-to-Intermediate
System (IS-IS) is the routing algorithm used by the ISO protocol suite.
T A B L E 2 . 3
Retains knowledge of
all possible routes
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