Each router takes a copy of the update message, updates its routing
tables, and forwards the update message to all neighboring routers. This ?¬‚ooding of the
update message is required to ensure that all routers update their databases before creating
an updated routing table that re?¬‚ects the new topology. Figure 4-6 shows how link-state
protocols determine routes.
Figure 4-6 Link-State Protocols
Examples of link-state routing protocols are Open Shortest Path First (OSPF) and
Intermediate System??“to??“Intermediate System (IS-IS).
NOTE Cisco developed the Enhanced Interior Gateway Routing Protocol (EIGRP),
which combines the best features of distance vector and link-state routing protocols.
Link-State Packets
SPF
Algorithm
Routing
Table
Topological
Database
Shortest Path First Tree
246 Chapter 4: LAN Connections
Summary of Exploring the Functions of Routing
The following list summarizes the key points that were discussed in the previous sections:
?– Routers have certain components that are also found in computers and switches. These
components include the CPU, motherboard, RAM, and ROM.
?– Routers have two primary functions in the IP packet delivery process: maintaining
routing tables and determining the best path to use to forward packets.
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