DK

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)