Access List (ACL)

In Cisco Packet Tracer, an access list is a network security feature used to control and filter traffic based on specified criteria. It allows you to permit or deny traffic flow based on factors such as source/destination IP addresses, protocols, port numbers, and other parameters. Access lists are commonly used to enforce security policies, control network traffic, and protect network resources.

To use access lists in Cisco Packet Tracer, follow these steps:

Access the CLI of the router or switch: Double-click on the router or switch in Packet Tracer to access its Command Line Interface (CLI).
Enter global configuration mode: Enter the following command to access the global configuration mode:

configure terminal

Create an access list: Use the following command to create an access list:

access-list <access-list-number> <permit|deny> <source> <destination> <protocol>

Replace <access-list-number> with the desired access list number, <permit|deny> to specify whether to permit or deny the traffic, <source> with the source IP address or network, <destination> with the destination IP address or network, and <protocol> with the protocol (e.g., IP, TCP, UDP) you want to filter.
Apply the access list to an interface: To apply the access list to an interface, use the following command:

interface <interface-type> <interface-number>

ip access-group <access-list-number> <in|out>

Replace <interface-type> with the specific interface type (e.g., FastEthernet, GigabitEthernet), <interface-number> with the interface number (e.g., 0/0, 1/1), <access-list-number> with the access list number you created, and <in|out> to specify whether to apply the access list inbound or outbound on the interface.
Save and exit: Save the configuration changes and exit the CLI using the following commands:

end

copy running-config startup-config

This will save the configuration to non-volatile memory, ensuring that the configuration persists upon device reboot.

By following these steps, you can create and apply access lists in Cisco Packet Tracer to control and filter network traffic based on specific criteria. Remember to adjust the specific commands and parameters according to your network requirements and the devices being configured.

Note: Cisco Packet Tracer is a network simulation tool, and the access list functionality may have limitations compared to real-world Cisco devices. It's always recommended to consult the official Cisco documentation or seek guidance from experienced professionals for accurate configuration and usage of access lists in production environments.

Here is an example of an ACL

Enable

Conf t

Ip access-list standard st1

Deny 192.168.10.0 0.0.0.255

Permit any

Exit

Int g0/0/2

Ip access-group st1 out