An access control list (ACL) is an important component of network security. It is a list of permissions that decide what types of traffic are allowed to enter or exit a network.
Standard ACLs are the most common type of ACLs and are used to filter traffic based on source and destination IP addresses. A standard ACL can be either a numbered or named ACL. A numbered ACL has a range of 1-99 or 1300-1999. A named ACL can have any name you choose.
When configuring a standard ACL, you will need to specify a range of IP addresses. The range can be either a host IP address or a network IP address. You will also need to specify the type of traffic that should be allowed or denied. For example, you can allow all traffic from a specific IP address or you can deny all traffic from a specific IP address.
The ACLs are divided into two types: standard ACLs and extended ACLs. In this Article, we will be focusing on standard ACLs. We will go over what they are, their range, examples, and configuration. By the end of this guide, you will have a good understanding of standard ACLs and their purpose.
In the previous blog of our CCNA 200-301 series , we talked about the RSTP Protocol in networking. I recommend you go through it before you jump to this blog.
What are standard ACLs?
Standard ACLs are access control lists that define which traffic is allowed to travel and cross a network. They are used to filter traffic based on source and destination IP addresses. A standard ACL can be either a numbered or named ACL. A numbered ACL has a range of 1-99 or 1300-1999.
A named ACL can have any name you choose.
A standard ACL is configured on an interface and can be applied to both inbound and outbound traffic. When a packet enters an interface, the ACL filters the packet against a set of rules. If the packet matches the rules, it is either allowed or denied. If the packet does not match any rules, the access list is ignored and the packet is allowed.
By using standard ACLs, you can control which traffic is allowed to travel through a network. This includes limiting access to specific services, blocking malicious traffic, or allowing only certain types of traffic. Standard ACLs can also be used to apply ACLs to different types of traffic, such as TCP or UDP.
Why use standard ACLs?
Standard ACLs are the most commonly used type of ACL and are used for controlling and monitoring the traffic flowing through a network. They provide a way to block unwanted traffic, restrict access to certain services, and ensure the security of a network.
Standard ACLs are also a good way to ensure that only certain types of traffic can access specific services or applications. For example, email traffic can be restricted to certain networks and FTP traffic can be restricted to certain IP addresses. This ensures that only authorized users can access the services and applications.
Standard ACLs can also be used to monitor traffic on a network. They allow an administrator to review what types of traffic are entering and leaving a network and to identify and block any malicious traffic. This helps keep a network safe and secure.
How to configure standard ACLs?
Once you have decided to use a standard ACL, the next step is to configure it. Configuring a standard ACL involves the following:
- Specifying a range of IP addresses
- The type of traffic to be allowed or denied
- The direction of the traffic which could either be inbound or outbound
The first step is to identify which IP addresses you want to allow or block. The range of IP addresses can be either a single host IP address or a network IP address. You will also need to specify the type of traffic you want to allow or deny. This can be any type of traffic, such as UDP, TCP, ICMP, or ARP. Once you have identified the IP address range and type of traffic, you can create an access list entry.
An access list entry consists of a number, a permit or denies action and the source and destination IP addresses. For example, an entry may look like this: 5 deny 10.1.1.0/24. This will deny all traffic from the 10.1.1.0/24 network.
Once you have created your access list entries, the next step is to apply the access list to an interface. This is done with the “ip access-group” command. For example, “ip access-group 5 in” will apply access list 5 to the inbound traffic on the interface.
Finally, you can verify that the access list is working properly by using the “show ip access-lists” command. This will show you a list of the access list entries and the number of packets that were matched.
How to Test standard ACLs?
Once you have configured your standard ACL, you will need to test it to make sure it is working properly. To test a standard ACL, you can simply use some traffic sources to generate network traffic and then use a packet sniffer to monitor the traffic.
A packet sniffer such as Wireshark can be used to monitor the traffic on a network. This will show you which packets are being dropped and which packets are being allowed. You can also use a port scanner such as Nmap to scan the network and see which ports are open and closed.
Troubleshooting standard ACLs
If you encounter any problems with your standard ACL, there are several steps you can take to troubleshoot them.
- The first step is to make sure that the ACL is configured properly. Make sure that the entries are in the correct order and that the source and destination addresses are correct.
- The next step is to verify that the rules are being applied correctly. You can do this by using the “show ip access-list” command. This will show you the access list entries and the number of packets that were matched.
- If the access list is configured correctly but the traffic is still not being blocked or allowed, you may need to check the router or switch’s log to see if there are any error messages related to the ACL.
- You can also check the router’s ARP table to make sure the traffic is being routed correctly.
Conclusion
Standard ACLs are a powerful way to control and monitor network traffic. With standard ACLs, you can control which traffic is allowed to traverse a network, restrict access to certain services, and monitor the traffic. By following the steps outlined above, you can configure and test your standard ACLs to make sure they are working properly.
In the upcoming blog, we will learn about extended ACLs and compare them to standard ACLs.
Stay tuned for more blogs for the CCNA 200-301 series!
