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Routing is the process of establishing the routes that data packets must follow to reach their destination. In this process, a routing table is created which contains information regarding routes that data packets follow. Various routing algorithms are used for the purpose of deciding which route an incoming data packet needs to be transmitted on to reach the destination efficiently. 

The challenge is transferring data from one node in one network to another node in a different network

Routers

Routers examine the destination IP address of a received packet and make routing decisions accordingly. To determine which interface the packet will be sent to, routers use routing tables. A routing table lists all the networks for which routes are known. Each router’s routing table is unique and stored in the RAM of the device.

Routing Table

A routing table is a set of rules, often viewed in a table format, that is used to determine where data packets traveling over an Internet Protocol (IP) network will be directed.

All IP-enabled devices, including routers and switches, use routing tables.

The routing table contains the information needed to forward a packet along the best path toward its destination. Each packet contains information about its origin and destination. The Routing Table provides the device with instructions for sending the packet to the next hop on its route across the network.

Routing table entries are

Entry

Purpose

Network ID

The next ID/destination on the route

Subnet Mask

The subnet mask that is used to match the destination IP address to the Network ID

Next Hop

The IP address to where the packet is forwarded

Outgoing Interface (ethernet card)

The outgoing ethernet card from which the packet should leave this router

Metric

Typically used to say maximum number of allowed hops

Routing Table Example

Routing Algorithms

Routers use algorithms to determine how routing tables are populated and used. These can be

  • Fixed

  • Flooding

  • Adaptive

  • Non-adaptive

Fixed Algorithms

For each node in the network, the route is predefined in the routing tables. Changes to the route can only be achieved by changing the topology and the routing tables.

Flooding Algorithms

Adaptive Algorithms

Non-Adaptive Algorithms

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