2.1 Networks including the Internet

Router Function and Role

A router is a fundamental device in computer networks, acting as a traffic director between different networks. Its primary function is to forward data packets between networks, ensuring they reach their intended destination. Routers are essential for connecting home and office networks to the internet and for facilitating communication between various networks within a larger organization.

Core Function: Packet Forwarding

The core function of a router is to examine the destination address of incoming data packets and determine the best path to forward them. This process involves looking at the network address and subnet mask of the destination.

How a Router Works

1. Receiving a Packet: A router receives a data packet from one network interface.
2. Examining the Destination Address: The router examines the destination IP address in the packet's header.
3. Routing Table Lookup: The router consults its routing table. This table contains information about different networks and the best paths to reach them.
4. Path Determination: Based on the destination address and the routing table, the router determines the next hop ÔÇô the next router or network to forward the packet to.
5. Packet Forwarding: The router forwards the packet to the determined next hop.

Key Components and Concepts

Several key components and concepts are crucial to understanding how routers operate:

• IP Addresses: Routers rely on IP addresses to identify devices and networks.
• Subnet Masks: Subnet masks help routers determine which part of an IP address represents the network and which part represents the host.
• Routing Table: A table containing information about networks and the best paths to reach them. Routing tables can be static (manually configured) or dynamic (learned through routing protocols).
• Next Hop: The next router or network to which a packet should be forwarded.
• Default Gateway: The router that acts as the gateway to other networks, including the internet.

Types of Routers

Routers come in various forms, each designed for different purposes:

• Home Routers: Typically used to connect a home network to the internet. They often combine routing, wireless access point, and firewall functionalities.
• Business Routers: More robust and feature-rich routers used in business networks, offering higher performance and security.
• Core Routers: High-performance routers used in internet service provider (ISP) networks to route traffic between different networks.

Routing Protocols

Routers use routing protocols to communicate with each other and dynamically update their routing tables. Some common routing protocols include:

• RIP (Routing Information Protocol): A distance-vector routing protocol.
• OSPF (Open Shortest Path First): A link-state routing protocol.
• BGP (Border Gateway Protocol): Used for routing between different autonomous systems (AS) on the internet.

Table: Router Components

In summary, routers are essential for network communication, acting as intelligent traffic directors that ensure data packets reach their intended destinations efficiently and reliably. They utilize routing tables and protocols to make informed forwarding decisions.