What is a router? How does it work?

by Amara Lite · March 5, 2024

What is a router?

A router is a traffic cop or a mail sorter on the expansive internet highway, managing the flow of information among a diverse network of connected devices, including computers, smartphones, servers, and various gadgets, as they communicate with each other to share information.

A router also serves as a gateway to the internet. In networking terms, a gateway is a device that connects different networks, facilitating communication between them. Example: In your home setup, your local area network (LAN) consists of the devices that are within your home, such as your computers, smartphones, and smart TV’s , and the internet is a separate network (a bigger network). Now, the router acts as a gateway by connecting your home network to the internet.

When your devices want to access something on the internet, they send their requests to the router. The router, acting as a gateway, forwards these requests to the internet and receives the responses, directing them back to the appropriate devices on your home network.

In summary, the router is both a traffic manager for data within your home network and a gateway that connects your home network to the broader network, which is the internet.

How does a router work?

Here’s a simplified overview of how a router works:

Packet Reception:The router receives data packets from different devices. They operate at the network layer (Layer 3) of the OSI model, and they receive data packets from devices connected to their local network or from external networks.

Packet Inspection:Upon receiving a packet, the router examines the header information, including the source and destination IP addresses. This analysis is crucial for making routing decisions.

Routing Decision: Based on the destination IP address, the router consults its routing table, which is a set of rules or protocols, to determine the best path for the packet based on its destination IP address. The routing table is often dynamically updated using routing protocols like RIP, OSPF, or BGP

Path Determination: After determining the best path, the router selects the appropriate outgoing interface or port through which the packet should be forwarded

Packet Forwarding: The router forwards the packet to the next hop or network along the determined path. This process may involve multiple routers cooperating to guide the packet to its final destination.

Repeat Process: Steps 1–5 are repeated for each packet that the router handles, allowing it to efficiently manage the flow of data between devices and networks.

Network Address Translation (NAT)

IP Address Mapping:

NAT translates the private IP addresses of devices on a local network to a single public IP address (and vice versa) for all outgoing/incoming Internet traffic. This is done by maintaining a NAT translation table that keeps track of internal devices’ private IP addresses and their corresponding public IP address translations.

Port Address Translation (PAT):

Often used alongside NAT, PAT allows multiple devices on a local network to be mapped to a single public IP address with different ports. This is how multiple devices can share a single public IP address but still maintain unique sessions on the Internet.

Firewall Functionality

Traffic Filtering:

Routers with firewall capabilities can inspect the incoming and outgoing packets based on predefined security rules. These rules can include allowances or blocks based on IP addresses, domain names, protocols, and ports. By applying these rules, routers can prevent unauthorized access and protect the network from potential threats.

Stateful Packet Inspection (SPI):

More advanced routers may perform Stateful Packet Inspection (SPI), which not only examines the packet headers (like traditional packet filtering) but also keeps track of the state of active connections. SPI allows the firewall to distinguish between legitimate packets for different types of connections and potentially harmful packets attempting to exploit vulnerabilities.

Intrusion Detection and Prevention:

Some routers go beyond basic firewall functionality and include intrusion detection systems (IDS) and intrusion prevention systems (IPS). These systems analyze network traffic to detect and respond to suspicious activities by logging information, blocking traffic, or alerting administrators.

Error Handling

Routers incorporate error-checking mechanisms to handle issues such as packet loss, network congestion, or failures. They may implement protocols like TCP (Transmission Control Protocol) that include error-checking and retransmission mechanisms to ensure reliable data transfer.

With these functions, routers act as the backbone of network security and connectivity, managing data flow between different networks and the Internet, ensuring data is routed efficiently, and protecting networks from unauthorized access and threats.

Here’s also a link to the youtube video: