Cisco Packet Tracer Fundamentals

Cisco Packet Tracer Basics

  • Introduction to Cisco Packet Tracer (CPT) and its use for creating network labs.
  • Objective: Familiarize users with the software interface and basic functionalities.

Creating a Simple LAN

  • Accessing Devices:
    • Network devices (routers, switches, hubs, wireless devices, firewalls) are located at the bottom of the CPT interface.
    • End devices (PCs, laptops, servers) can also be selected from the bottom.
  • Adding a Switch:
    • Click on network devices, choose a switch (e.g., 2950 24-port switch), and drag it to the workspace.
  • Adding Computers:
    • Click on end devices and drag PCs or laptops to the workspace.
  • Connecting Devices:
    • Use the "Connections" option (zigzag signal) to connect devices with wires.
    • The software can automatically select the appropriate wire type.
    • A black wire indicates a straight cable connection.
  • Initial Login:
    • Choose "Cisco Skills for All" when prompted during CPT startup.
    • Troubleshooting login issues: Close internet, start CPT, then restart the internet.

Practical Exercise: Building a LAN

  • Drag a switch and several computers to the workspace.
  • Connect the computers to the switch using automatic connection wires.
  • Click on each device and then the switch port to establish the connection.

Editing and Deleting Devices

  • Deleting Devices:
    • Use the cross symbol at the top to delete devices or connections.
    • Click the cross, then click the item to be deleted.
  • Exiting Delete Mode:
    • Use the escape symbol (first icon at the top) to return to the normal cursor.

Adding IP Addresses to Devices

  • Adding Labels:
    • Use the clipboard icon to add text labels for IP addresses near each computer.
    • Example IP addresses: 10.0.0.1, 10.0.0.2, 10.0.0.3, 10.0.0.4.
  • Configuring IP Addresses:
    • Click on a computer, go to the "Desktop" tab, and select "IP Configuration."
    • Choose "Static" to manually assign an IP address.
    • Enter the IP address (e.g., 10.0.0.1) and subnet mask (e.g., 255.0.0.0 for Class A).
    • Leave the default gateway and DNS server fields blank for a simple LAN.
  • Repeat the IP configuration for each computer, incrementing the last octet of the IP address.
  • Hover the mouse over a computer to view its configured IP address.

Testing the LAN with Ping

  • Accessing Command Prompt:
    • Click on a computer, go to the "Desktop" tab, and select "Command Prompt."
  • Using Ping Command:
    • Type ping followed by the destination IP address (e.g., ping 10.0.0.4).
    • Successful replies indicate that the LAN is working correctly.
  • Test connectivity by pinging all other computers in the LAN.

Customizing the Packet Tracer Interface

  • Showing Port Labels:
    • Go to "Options" > "Preferences."
    • Check the box for "Always show port label in the logical workspace" to display interface names (e.g., FA0/1, FA0/2).
  • Adjusting Font Size:
    • In preferences, increase the font size for better visibility.
    • Adjust font sizes for the main interface and CLI for improved readability.

Creating a LAN Using DHCP

  • Adding a Server:
    • Drag a server from the end devices to the workspace.
  • Configuring the DHCP Server:
    • Assign a static IP address to the server (e.g., 20.0.0.1).
    • Go to the "Services" tab, select "DHCP," and turn the service "on."
    • Configure the DHCP pool: set the default gateway (if needed), start IP address, maximum number of addresses, and DNS server (if needed).
  • Configuring Computers to Use DHCP:
    • For each computer, go to "IP Configuration" and select "DHCP."
    • The computer will automatically receive an IP address from the DHCP server.
  • DHCP Process (DORA):
    • Discover: Client broadcasts a request for a DHCP server.
    • Offer: DHCP server offers an IP address to the client.
    • Request: Client requests offered IP address.
    • Acknowledge: DHCP server acknowledges and assigns the IP address to the client.

Practical Scenario: DHCP in an Enterprise Network

  • Branch Office:
    • A small office with a few computers using a DHCP server for IP address assignment.
  • Head Office:
    • A larger office with many users. The company decides to move the DHCP server from the branch office to the head office.
  • Problem:
    • After moving the DHCP server, computers in the branch office no longer receive IP addresses.
  • Reason:
    • DHCP uses broadcast packets for the discovery process. Routers do not forward broadcast packets by default, thus preventing the DHCP requests from reaching the server in the head office.
  • Solution: DHCP Relay Agent
    • Configure a DHCP Relay Agent on the router in the branch office.
    • The Relay Agent converts the broadcast DHCP requests into unicast packets, which can be forwarded to the DHCP server in the head office.
    • The DHCP server then responds to the Relay Agent, which forwards the IP address to the client.

Introduction to Routers

  • Connecting a Router and a Computer:
    • Connect a router to a computer using a cable.
  • Router Operating System (iOS):
    • Routers use an Internetwork Operating System (IOS).
  • Configuration Methods:
    • Command Line Interface (CLI)
    • Graphical User Interface (GUI)
  • Focus on CLI configuration first to understand the underlying commands and concepts.

CLI Configuration Modes

  • User Mode:
    • Limited functionality, mostly for viewing basic information.
    • Prompt: Router>
  • Privileged Mode:
    • Allows more advanced commands and configuration.
    • Enter by typing enable
    • Prompt: Router#
  • Configuration Mode:
    • Used to configure router settings.
    • Enter by typing config terminal or config t
    • Prompt: Router(config)#
  • Configuration Interface Mode:
    • Used to configure specific interfaces.
    • Enter by typing interface <interface-name> (e.g., interface FastEthernet0/0)
    • Prompt: Router(config-if)#

Basic Router Configuration

  • Accessing CLI:
    • Click on the router, then go to the "CLI" tab.
  • Navigating Configuration Modes:
    • Type enable to enter privileged mode.
    • Type config terminal to enter configuration mode.
    • Type interface <interface-name> to enter interface configuration mode.
  • Assigning an IP Address to an Interface:
    • Use the command ip address <ip-address> <subnet-mask> in interface configuration mode (e.g., ip address 10.0.0.1 255.0.0.0).
  • Enabling an Interface:
    • By default, interfaces are in a shutdown state.
    • Use the command no shutdown to enable the interface.
  • Exiting Configuration Modes:
    • Use the command exit to move one step back.

Example Configuration

  • Configuration Steps:
    • Enter privileged mode: enable
    • Enter configuration mode: config t
    • Enter interface configuration mode: interface FA0/0
    • Assign IP address: ip address 10.0.0.1 255.0.0.0
    • Enable interface: no shutdown
    • Exit interface configuration mode: exit
    • Exit configuration mode: exit
  • Configuring the Computer:
    • Assign a static IP address (e.g., 10.0.0.2) and subnet mask (e.g., 255.0.0.0).
    • Set the default gateway to the router's IP address (e.g., 10.0.0.1).
  • Testing Connectivity:
    • Use the ping command on the computer to ping the router's IP address.
    • Use the ping command on the router to ping the computer's IP address.

GUI Configuration

  • Accessing GUI:
    • Click on the router, then go to the "Config" tab.
  • Configuring Interfaces:
    • Select the interface (e.g., FastEthernet0/0) in the GUI.
    • Check the "Port Status" box to enable the interface (equivalent to no shutdown).
    • Enter the IP address and subnet mask in the appropriate fields.
  • GUI simplifies the configuration process, but CLI is essential for advanced configurations and troubleshooting.