Understanding Routers: A Comprehensive Guide to Networking

This tutorial covers essential networking concepts, including circuit switching vs. packet switching, TCP/IP protocol fields, ARP/RARP protocol fields, IP addresses, MAC addresses, and networking devices like hubs, switches, bridges, routers, gateways, and firewalls.

Here’s a breakdown of what we’ll cover:

• Circuit Switching vs. Packet Switching
• LAN vs. WAN vs. MAN
• What is an IP address?
• What is a MAC Address?
• Basics of OSI and TCP-IP Layers
• What is a Hub?
• What is a Switch?
• What is a Bridge?
• What is a Router?
• What is a Gateway?
• Firewall basics
• TCP-IP Packet format
• ARP Protocol format

What is a Router?

A router is a networking device that connects two or more networks. It operates at Layer 3 of the OSI model (the network layer). Routers enable internetworking between dissimilar sub-networks.

Essentially, the router must perform these key functions:

1. Provide a Link Between Networks: Acts as the bridge connecting different network segments.
2. Route Data: Handles the routing of data between processes running on different networks, ensuring the delivery of data.
3. Enable Interoperability: Sub-network architectures don’t need to be modified to allow communication between different networks.

Let’s delve into how a router achieves internetworking with an example:

Router Internetworking Example: ATM to LAN

Consider a scenario where a server connected to an ATM network needs to communicate with a workstation connected to an 802.11 LAN.

The router, in this case, has protocols up to Layer 3 for both ATM and LAN networks. It manages the communication between the server and the workstation.

1. Server to Workstation: When a TCP/IP packet arrives at the router from the server, the router removes the ATM protocol headers. It then inserts LAN-compatible headers from Layer 1 to Layer 3 and forwards the packet to the LAN network.

2. Workstation to Server: Conversely, when a TCP/IP packet comes from the workstation, the router removes the LAN protocol headers, adds ATM-compatible headers from Layer 1 to Layer 3, and passes the packet to the ATM network.

The following figure illustrates the protocol stacks at the ATM-based server, LAN-based workstation, and the router:

(This figure is adapted from a book by William Stallings)

Modern Routers

Today, routers are available for the latest broadband technologies, like LTE and WiMAX, and handle interworking to allow different networks to communicate.

Router Vendors

• WLAN (Wi-Fi): Check out popular Wi-Fi router suppliers like DLINK, Linksys, and Netgear for their technical specifications.
• LTE-WiMAX: Explore suppliers of LTE and WiMAX routers, including those capable of interfacing WiMAX networks on one side and LTE on the other.