Free CCNA | Standard ACLs | Day 34 | CCNA 200-301 Complete Course

Introduction

This tutorial provides a comprehensive guide to understanding standard Access Control Lists (ACLs) as part of the CCNA 200-301 curriculum. ACLs are essential for network security and traffic management in Cisco devices. By following these steps, you will gain a solid foundation in ACL concepts, their operation, and practical implementations.

Step 1: Understanding ACLs

• Definition: Access Control Lists (ACLs) are a set of rules that control the flow of traffic in and out of a network interface.
• Purpose: They help in filtering traffic based on specified criteria, such as IP addresses.
• Common Uses:
  • Restricting access to network resources
  • Allowing or denying specific traffic types

Step 2: How ACLs Work

• Traffic Filtering: ACLs evaluate packets based on source and destination IP addresses, protocols, and ports.

• Process Flow:

  1. A packet arrives at the router.
  2. The router checks the packet against the ACL rules.
  3. Depending on the match, the packet is either allowed or denied.

• Implicit Deny: At the end of every ACL, there is an implicit 'deny all' rule. This means that if a packet does not match any of the defined rules, it will be denied access by default.

Step 3: Types of ACLs

• Standard ACLs:

  • Filter traffic based solely on the source IP address.
  • Range: 1-99 (numbered) or named (e.g., 'my_access_list').

• Extended ACLs:

  • Filter traffic based on source and destination IP addresses, protocols, and ports.
  • Range: 100-199 (numbered) or named.

Step 4: Configuring Standard Numbered ACLs

1. Access the Device:

   • Log in to your Cisco router or switch.

2. Enter Configuration Mode:

   configure terminal
   

3. Create the ACL:

   access-list [number] [permit|deny] [source] [wildcard]
   

   • Example:

   access-list 10 permit 192.168.1.0 0.0.0.255
   

   • This rule permits traffic from the 192.168.1.0 network.

4. Apply the ACL to an Interface:

   interface [interface_type] [interface_number]
   ip access-group [number] [in|out]
   

   • Example:

   interface GigabitEthernet0/1
   ip access-group 10 in
   

Step 5: Configuring Standard Named ACLs

1. Access the Device:

   • Log in to your Cisco router or switch.

2. Enter Configuration Mode:

   configure terminal
   

3. Create the Named ACL:

   ip access-list standard [name]
   permit [source] [wildcard]
   

   • Example:

   ip access-list standard my_acl
   permit 192.168.1.0 0.0.0.255
   

4. Apply the Named ACL to an Interface:

   interface [interface_type] [interface_number]
   ip access-group [name] [in|out]
   

   • Example:

   interface GigabitEthernet0/1
   ip access-group my_acl in
   

Conclusion

In this tutorial, we covered the fundamental concepts of standard ACLs, how they function, and how to configure both numbered and named ACLs on Cisco devices. Understanding and implementing ACLs is crucial for managing network security effectively. For further practice, consider setting up different ACL scenarios in a lab environment to reinforce your learning.