Optimal path determination
The determination of the optimal path is based on different standards of measurement, for example, path length, and metric. Routing algorithms calculate path indexes to determine the optimal path to destination.
To facilitate the process of path determination, routing algorithms initialize and maintain routing tables, which contain the routing information. This information changes depending on the routing algorithm used.
Routing algorithms fill in routing tables with different information. “Destination/next hop” combinations tell a router that a destination can be reached through the shortest path by sending a packet to a particular router representing the “next hop” on the way to the final destination. When the router receives an incoming packet, it checks the destination address and makes an attempt to associate this address with a next hop. An example of a routing table is shown below.
Destination address | Next hop |
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27 | Router A |
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57 | Router B |
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17 | Router C |
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24 | Router A |
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52 | Router A |
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16 | Router B |
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26 | Router A |
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Routing table also contain other information. “Metrics” represent information about the desirability of a path or a route. Routers compare metrics to determine the optimal routes. Metrics differ depending on the routing algorithms being used. A variety of common metrics will be described below in this chapter.
Routers communicate with each other (and maintain their routing tables) by transmitting various messages. One of these messages is the “routing update”. The routing update usually includes all or a part of a routing table. By analyzing routing update information from all routers, any router can build a detailed picture of network topology. Another example of a message exchange between routers is a
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