Definition

It is a network device that forwards data between different networks, typically connecting local networks to external networks.

It directs data packets between these networks by determining the best path for the data to travel.

Functions

Routing

Routers use IP addresses to determine best path for forwarding packets between networks.

Routers maintain a routing table, which maps network destinations and the paths to reach them. Routing tables are dynamically updated using protocols like:

• RIP (Routing Information Protocol)
• OSPF (Open Shortest Path First)
• BGP (Border Gateway Protocol)

Routers can use both static and dynamic routes (learned via routing protocols).

Network Address Translation (NAT)

Enables multiple devices on a local network to share single public IP address.

Many devices in one network can use the router's public IP to access the internet. Requests are forwarded through this router and responses are sent to the appropriate device in the local network.

NAT helps conserve IPv4 addresses and provides basic security by hiding internal IP addresses from the outside world.

Firewall & Security Features

Access Control Lists (ACLs)

Routers often have ACLs, which allow administrators to permit or deny traffic based on specific rules.

Rules are typically based on IP addresses, port numbers, or protocols (eg. allowing web traffic while block certain applications).

Stateful Packet Inspection (SPI)

Many routers perform SPI that inspects incoming and outgoing packets to ensure they are part of a valid connection.

VPN Support

Routers include support for Virtual Private Networks (VPNs) that allow secure and encrypted communication between two remote networks.

VPN protocols like IPSec or OpenVPN are often supported.

Dynamic Host Configuration Protocol (DHCP)

Most routers act as DHCP servers that dynamically assign IP address to devices on the network.

Dual-Band and Tri-Band Wi-Fi

Modern routers are dual-band in 2.4GHz and 5 GHz, or tri-band in one 2.4GHz and two 5GHz bands.

This allows routers to balance network load and reduce interference by allocating devices to appropriate frequency band.

Quality of Service (QoS)

Allows routers to prioritise traffic based on certain types of data.

Routers can classify packets and assign priority, ensuring that bandwidth-sensitive applications like VoIP or video streaming get higher priority than regular data.