Networking Devices

Routers

• Routers connect different networks and perform routing, forwarding packets from one network to another.
• They are used in WAN (Wide Area Network) scenarios, like connecting offices in different geographical locations (e.g., India and the US).
• Routers connect a LAN (Local Area Network) to other networks, enabling machines in one LAN to communicate with machines in another.
• The concept of communication between different networks is called inter-networking.
• Default Gateway: The interface connecting a LAN to a router. Computers in the LAN use the IP address of this interface to send packets outside their local network.
  • Example: If the router's interface IP is 10.0.0.1, computers in the LAN (e.g., 10.0.0.2, 10.0.0.3, 10.0.0.4) use 10.0.0.1 as their default gateway.

Cisco Packet Tracer

• Cisco Packet Tracer is a free software used for network simulation and practical practice.
• It allows users to create and configure network devices and connections.

LAN Setup in Packet Tracer

• Connecting computers using a switch creates a LAN.
• IP addresses are needed for computers to communicate within the LAN.
• In a LAN, a default gateway configuration is not mandatory.
  • If a computer only needs to communicate with other devices within the LAN, the default gateway can be left unconfigured.
• The ping command is used to check network connectivity between devices.
• Switches create a MAC address table to forward packets efficiently within the LAN using unicasting.

Adding a Router to the Network

• Adding a router and connecting it to the switch introduces the concept of a default gateway.
• Computers in the LAN need to be configured with the IP address of the router's interface (connected to the LAN) as their default gateway to communicate outside the LAN.
• The default gateway IP address is the same for all computers in the LAN that need to communicate externally.

Router's Role in Path Selection

• Routers determine the best path to forward packets from source to destination, especially in networks with multiple routers.
• Routers use routing protocols to calculate the best path based on different parameters.

Router Components

• Different router models exist (e.g., Cisco 2501).

• Key components include:

  • AUI (Attachment Unit Interface): Connects the router to the LAN (via a switch).
  • Serial Ports (S0, S1): Used for WAN connectivity, connecting routers to each other.
  • Console Port: Used for router configuration and programmability.
  • Auxiliary Port: Similar to the console port, used for configuration.
  • On/Off Button: Power switch.
  • Power Supply: Provides power to the router.

Fixed vs. Modular Routers

• Routers are divided into two categories: fixed-end routers and modular routers.

Fixed-End Routers

• Fixed-end routers have a fixed number of ports (e.g., two serial ports in the 2501 model).
• If the number of required connections exceeds the available ports, the router needs to be replaced with a model having more ports.
• Example: Upgrading from a router with two serial ports (2501) to one with four serial ports (2520) to accommodate more WAN connections.
• This can become costly and inefficient as the network grows.

Modular Routers

• Modular routers allow adding or removing modules to increase or decrease the number of ports as needed (scalability).
• They have slots for adding different types of modules, such as serial port modules.
• Example: Cisco 2620 router with available module slots.
• Adding a two-port serial module (WIC-2T) increases the router's WAN connectivity by two ports.
• Modular routers are preferred because they offer scalability and avoid the need to replace the entire router when more ports are required.

Operating Systems on Network Devices

• Like computers, network devices (switches and routers) have operating systems.
• Cisco devices use an Internetwork Operating System (IOS).

Wireless Networks and Access Points

• Wireless access points (APs) or wireless routers are used to provide wireless connectivity.
• Typically used in homes and small offices to provide Wi-Fi.
• The access point connects to the ISP (Internet Service Provider) via a wired connection (WAN port) and provides wireless access to devices within its range.
• Devices connecting wirelessly also need IP addresses.

DHCP (Dynamic Host Configuration Protocol)

• DHCP is a protocol that automatically assigns IP addresses to devices in a network.
• Two ways of assigning IP addresses:
  • Static: Manually configuring IP addresses on each device.
  • DHCP: Automatically assigning IP addresses using a DHCP server.
• In large networks, a dedicated DHCP server is used to manage IP address allocation.
• In home networks, the wireless router typically acts as a DHCP server.
• The DHCP server assigns IP addresses, subnet masks, default gateways, and other network parameters to the devices.
• Example: A DHCP server assigning IP addresses in the 192.168.0.0/24 range to devices connecting to a wireless router.

Firewalls

• Firewalls protect networks from malicious traffic, such as viruses, malware, and hacking attempts.
• They can be implemented as operating system-based firewalls or as physical devices.
• Physical firewalls provide more robust protection than OS-based firewalls.
• Different companies offer firewall solutions (e.g., Cisco ASA, Fortinet, Palo Alto).
• Firewall configuration requires specialized training and expertise.

WAN Setup and Firewalls in Packet Tracer

• Connecting two routers in Packet Tracer requires serial ports.
• If a router doesn't have a serial port, a serial port module needs to be added.
• Firewalls can be added to the network to filter malicious traffic.

Summary of Network Devices

• Hubs
• Bridges
• Switches
• Routers
• Wireless Access Points
• Firewalls
• Servers (to be covered in detail later)