Router Basic


A router is a device that can connect two or more network segments. These are intelligent network devices that store information in its routing tables such as paths, hops, and bottlenecks. With this info, they are able to determine the best path for data transmission.

Router Functions

A router has two main functions:

  • Determining the best path to available networks
  • Forwarding traffic to those networks

The Routing Table

  • The best available path or paths to a destination network are listed in router’s routing table and will be used for forwarding traffic
  • A routing table consists of directly connected networks and routes configured statically by the administrator or dynamically learned through a routing protocol.

Dynamic vs Static Routes

There are two types of routing.

  • Static Routing
  • Dynamic Routing

Static Routing

Static routing is a form of routing that occurs when a router uses a manually-configured routing entry, rather than information from dynamic routing traffic. In many cases, static routes are manually configured by a network administrator by adding in entries into a routing table, though this may not always be the case. Unlike dynamic routing, static routes are fixed and do not change if the network is changed or reconfigured.

Dynamic Routing Protocols

  • When a routing protocol is used, routers automatically advertise their best paths to known networks to each other.
  • Routers use this information to determine their own best path to the known destinations.
  • When the state of the network changes, such as a link going down or a new subnet is added, the routers update each other.
  • Routers will automatically calculate a new best path and update the routing table if the network changes.

Dynamic Routing Protocol Advantages

  • The routers automatically advertise available subnets to each other without the administrator having to manually enter every route on every router.
  • If a subnet is added or removed the routers will automatically discover that and update their routing table.
  • If the best path to a subnet goes down routers automatically discover that and will calculate a new best path if one is available.

Dynamic Routing Protocols vs Static Routes

  • Routing protocols are more scalable than administrator defined static routes.
  • Using purely static routes is only feasible in very small environments.
Source: and Wikipedia

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