22.1 UNICAST ROUTING PROTOCOLS UNICAST ROUTING PROTOCOLS A routing table can be either static or dynamic. A static A routing table can be either static or dynamic. A static table is one with manual entries. A dynamic table is one table is one with manual entries. A dynamic table is one that is updated automatically when there is a change that is updated automatically when there is a change somewhere in the Internet. A routing protocol is a somewhere in the Internet. A routing protocol is a combination of rules and procedures that lets routers in combination of rules and procedures that lets routers in the Internet inform each other of changes. the Internet inform each other of changes.
22.2 Figure 22.12 Autonomous systems
•When it receives a packet, to which network should it pass the packet? •The decision is based on optimization: Which of the available pathways is the optimum pathway?
• One approach is to assign a cost for passing through a network. We call this cost a metric. • However, the metric assigned to each network depends on the type of protocol. • Some simple protocols, such as the Routing Information Protocol (RIP), treat all networks as equals. The cost of passing through a network is the same; it is one hop count. 22.4
22.6 Figure 22.13 Popular routing protocols
• In distance vector routing, the least-cost route between any two nodes is the route with minimum distance. • In this protocol, as the name implies, each node maintains a vector (table) of minimum distances to every node. • The table at each node also guides the packets to the desired node by showing the next stop in the route (next-hop routing). 22.7
22.8 Figure 22.15 Initialization of tables in distance vector routing
22.9 In distance vector routing, each node shares its routing table with its immediate neighbors periodically and when there is a change. Note
22.10 Figure 22.16 Updating in distance vector routing
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