Access Control Lists (ACLs) for CCNA: Creating Secure Networks

Access Control Lists (ACLs) are an important aspect of network security. They provide a mechanism for controlling the flow of network traffic based on various criteria, such as source and destination IP addresses, protocol type, and port numbers. In this blog post, we will explore the basics of Access Control Lists and how to implement them in a network. 
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What is an Access Control List (ACL)?

An Access Control List is a set of rules that determine which traffic is allowed to pass through a network device and which traffic is blocked. ACLs are typically implemented on routers and switches to control traffic flow between different network segments. ACLs can be applied to inbound or outbound traffic on an interface.

ACLs work by examining the headers of network packets and comparing them to the criteria specified in the ACL rules. If a packet matches a rule in the ACL, the device will either permit or deny the packet based on the action specified in the rule.

Types of ACLs

There are two main types of ACLs: standard and extended.

Standard ACLs are based on the source IP address only. They are typically used to block traffic from specific hosts or networks. Standard ACLs are numbered from 1 to 99 and 1300 to 1999.

Extended ACLs are based on a variety of criteria, including source and destination IP addresses, protocol type, port numbers, and more. They are used to permit or deny specific types of traffic between networks. Extended ACLs are numbered from 100 to 199 and 2000 to 2699. 
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Creating ACLs

To create an ACL, you first need to specify the type of ACL you want to create (standard or extended) and then define the criteria for the ACL rules. Here is an example of a standard ACL that blocks traffic from a specific host:

In this example, ACL 1 is a standard ACL that denies traffic from host 192.168.1.10 and permits all other traffic.

Here is an example of an extended ACL that permits HTTP traffic from a specific network:

In this example, ACL 101 is an extended ACL that permits TCP traffic from the 192.168.1.0/24 network to any destination on port 80 (HTTP). The second rule denies all other traffic. 
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Applying ACLs

After creating an ACL, you need to apply it to an interface. Here is an example of applying ACL 1 to the inbound interface of a router:

In this example, ACL 1 is applied to the inbound interface of FastEthernet 0/0.

Conclusion

Access Control Lists are an essential tool for securing network traffic. By defining rules for which traffic is allowed and which is blocked, ACLs can help prevent unauthorized access to network resources. When implementing ACLs, it's essential to carefully consider the criteria for each rule to ensure that legitimate traffic is not inadvertently blocked. With proper planning and implementation, ACLs can help create a secure and reliable network. best ccna training institute in pune