Hello again, in this guide, we’ll explore how to create a network using Cisco Packet Tracer, configure subnetting, and implement Access Control Lists (ACLs) to manage communication between subnets.

Introduction to Cisco Packet Tracer

Cisco Packet Tracer is a powerful network simulation tool designed for students, educators, and networking professionals. It allows users to create complex network topologies, configure devices, and visualize the network’s behavior without needing physical hardware.


Creating a Network with Subnetting

Step 1: Set Up the Network Topology

  1. Open Cisco Packet Tracer.
  2. Drag and drop the required network devices (e.g., routers, switches, PCs) onto the workspace.
  3. Connect the devices using appropriate cables (e.g., copper straight-through for different devices, crossover for similar devices).

Step 2: Configure the IP Addresses and Subnets

For this example, let’s create a network with two subnets:

Subnet A: 192.168.10.0/24
Subnet B: 192.168.20.0/24

Router Configuration:
  1. Access the router’s CLI:
Router> enable
Router# configure terminal

    2. Configure the interfaces:

Router(config)# interface GigabitEthernet0/0
Router(config-if)# ip address 192.168.10.1 255.255.255.0
Router(config-if)# no shutdown
Router(config-if)# exit

Router(config)# interface GigabitEthernet0/1
Router(config-if)# ip address 192.168.20.1 255.255.255.0
Router(config-if)# no shutdown
Router(config-if)# exit

    3. Configure DHCP on the router:
Router(config)# ip dhcp pool SUBNET_A
Router(dhcp-config)# network 192.168.10.0 255.255.255.0
Router(dhcp-config)# default-router 192.168.10.1
Router(dhcp-config)# exit

Router(config)# ip dhcp pool SUBNET_B
Router(dhcp-config)# network 192.168.20.0 255.255.255.0
Router(dhcp-config)# default-router 192.168.20.1
Router(dhcp-config)# exit


Step 3: Configure End Devices

  1. Assign IP addresses via DHCP to PCs:

    • PC1 (Subnet A): Set to DHCP

    • PC2 (Subnet B): Set to DHCP

    Ensure DHCP is enabled on both PCs and connect them to their respective subnets.

  2. Test connectivity:

    • Use the ping command to test communication between devices in different subnets.


Configuring Open Communication Between Subnets

At this stage, the network is configured such that devices in different subnets can communicate with each other freely. This setup is suitable for environments where unrestricted communication is necessary.

Implementing ACLs for Network Isolation

To isolate subnets and control traffic flow, we will implement ACLs.

Step 1: Define the ACLs

  1. Access the router's CLI:

    Router> enable
Router# configure terminal

  2. Create an ACL to deny traffic between subnets:

    Router(config)# access-list 100 deny ip 192.168.10.0 0.0.0.255 192.168.20.0 0.0.0.255
Router(config)# access-list 100 permit ip any any

Step 2: Apply the ACL to the Router Interfaces

  1. Apply the ACL to the inbound direction of the relevant interface:

    Router(config)# interface GigabitEthernet0/0
Router(config-if)# ip access-group 100 in
Router(config-if)# exit

Router(config)# interface GigabitEthernet0/1
Router(config-if)# ip access-group 100 in
Router(config-if)# exit

    2. Test connectivity:

    • Use the ping command to verify that devices in different subnets cannot communicate with each other.


Verify Configuration:

  1. Check ACLs:

    Router# show access-lists

  2. Check Interface ACL Application:

    Router# show ip interface gigabitEthernet0/0
Router# show ip interface gigabitEthernet0/1

The .pkt file can be downloaded here --> GitHub

Conclusion

In this guide, we've covered setting up a network using Cisco Packet Tracer, configuring subnetting, implementing DHCP for dynamic IP address assignment, and using ACLs to manage subnet communication. DHCP configuration ensures devices in each subnet receive IP addresses dynamically, streamlining network administration. Meanwhile, ACLs provide crucial subnet isolation, bolstering network security and governance. Mastery of these tools is essential for network administrators aiming to build robust, efficient, and secure networks. This is mr1diot signing off. Happy networking!