From the course: Cisco CCNA (200-301) Cert Prep: 3 Security, Automation, and Programmability

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Standard access control lists (ACLs)

Standard access control lists (ACLs)

From the course: Cisco CCNA (200-301) Cert Prep: 3 Security, Automation, and Programmability

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Standard access control lists (ACLs)

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- [Instructor] Access control lists, or ACLs, are utilized to identify IP addresses and ports for subnets or hosts. So I can match subnet 100.64/24 going anywhere, or I can match host 100.64.0.1 accessing anything on port 80, or I can match 100.64.0.1 source from TCP port 5231 going to host 100.65.65.1 on TCP port 443. I can get quite granular if I need to. While they can be used for filtering traffic on interfaces, they have many more uses. They can be used for matching traffic for QoS, or used for route filtering in dynamic protocols. When using ACLs for interface filtering, directionality is very important. An ACL is applied to an interface using either the keyword in or out. The way I remember which is which is to pretend I'm the router with my hands be the interfaces. For example, if my right hand is the interface I want to do the filtering on, I'll tell myself if I catch it in my hand, the interface, then use the in keyword, if the traffic is leaving through my right hand away…

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