What is a Router?

A router is a device that is used to connect multiple devices to a network and direct traffic between them. It is a networking device that forwards data packets between computer networks and is often used to connect devices such as computers, smartphones, and gaming consoles to the internet or to other devices within a network.

Routers typically use protocols such as TCP/IP to establish and maintain network connections, and can be configured to prioritize traffic or block unwanted traffic using features.

Dissecting Routers

Routers were initially developed by the United States government in the late 1960s and early 1970s as part of the Advanced Research Projects Agency Network (ARPANET) project, which was intended to create a secure and reliable communication network for military and government use. During the 1980s and 1990s, the rapid expansion of computer networks led to a wider availability of routers. This resulted in smaller businesses and individuals being able to access the benefits of network routing.

With the mass adoption of the internet in the late 1990s, the role of routers became more important as they were used to connect local area networks (LANs) to the internet and other WANs. This allowed computers to communicate with each other on a global scale. As networking technology evolved, routers took on more responsibilities, such as implementing security measures like firewalls.

Fundamental Parts of a Router

Although routers can be equipped with additional components for specialized functions such as Quality of Service (QoS) and virtual private networks (VPN), the following components are required for the proper functioning of a router.

• Network Interface: These are the physical ports on the router used to connect to different networks.
• Routing Table: A database that contains information about the various networks connected to the router and the best path to reach each of them.
• Memory: The router uses memory to store its configuration, routing table, and other critical information.
• Cooling System: Helps prevent the router from overheating and ensures that it runs smoothly.
• Management Interface: Allows administrators to configure and monitor the router's functions.

How a Router Works

The responsibilities of a router can be broken down into a series of steps that need to be carried out in the following order:

1. When a device on the network sends data, the data is broken down into smaller packets and sent across the network.
2. Each packet contains information about its destination, such as the IP address of the device it is trying to reach.
3. The router receives the packet and examines its header to determine the destination address.
4. The router consults its routing table, which contains information about the network topology and the most efficient path for packets to take to reach their destination.
5. The router forwards the packet to the appropriate device or network based on the information in its routing table.
6. If the destination device is on the same local network as the sending device, the router may use a technology called ARP (Address Resolution Protocol) to determine the MAC address of the destination device and forward the packet directly to it.
7. If the destination device is on a different network, the router may use a technology called NAT (Network Address Translation) to translate the source IP address of the packet to a public IP address that can be used to communicate with external networks.
8. The router may also use features such as Quality of Service (QoS) to prioritize certain types of traffic, such as video or voice data, over others.
9. The router can also act as a firewall, blocking incoming traffic that does not meet certain criteria and protecting the network from unauthorized access.
10. Devices on the network can connect to the router using Ethernet ports or Wi-Fi antennas, and the router may have a WAN (wide area network) port that is used to connect to the internet or another external network.

When networks are interconnected using multiple routers, they can communicate with each other about destination addresses by using a routing protocol. A routing table is then created by each router, which contains a list of routes between two computer systems on the interconnected networks.

• Control plane: Responsible for managing the device's control functions, such as routing protocols, network management, and configuration. It is the brain of the device and makes decisions on how to handle traffic based on the information it receives.
• Forwarding plane: Is responsible for the actual movement of data packets. It uses the information provided by the control plane to determine the optimal path for each packet and forwards them accordingly. The forwarding plane is designed for high-speed processing and is optimized for efficient packet forwarding.

Types of Routers

Routers are classified according to the networks in which they are used, and a source device must first initiate routing in order to send data to a destination.

Interior Router

Operates within a single organization's local area network (LAN). It handles the routing of data packets within the organization's network and uses interior gateway protocols (IGP) like OSPF (Open Shortest Path First) or RIP (Routing Information Protocol) to exchange routing information with other routers in the same network. An interior router maintains routing tables that list the paths to all destinations within the network.

Exterior Router

Operates on the Internet backbone, which connects different networks across the globe. It handles the routing of data packets between different networks and uses exterior gateway protocols (EGP) like BGP (Border Gateway Protocol) to exchange routing information with other routers in the Internet backbone. An exterior router maintains routing tables that list the paths to different networks and their subnets.

Border Router or Gateway Router

Connects a LAN with the Internet or a wide area network (WAN). It acts as a gateway for all incoming and outgoing traffic between the LAN and the external network. A border router uses both interior and exterior gateway protocols to exchange routing information. Routers then exchange routing information using gateway protocols to ensure that all routers have the same information.