Access Control Lists (ACLs) are crucial for managing traffic flow and enhancing security within a network. They are essentially a set of rules that are applied to a network interface, allowing or denying traffic based on specified criteria such as IP addresses, protocols, or ports.

Types of ACLs

There are two primary types of ACLs: Standard and Extended.

• Standard ACLs: These are simpler and only filter traffic based on the source IP address. They are identified by numbers ranging from 1 to 99 and 1300 to 1999¹.

• Extended ACLs: These are more complex and can filter based on source and destination IP addresses, IP protocols, ports, and other parameters. They are identified by numbers ranging from 100 to 199 and 2000 to 2699¹.

Applying ACLs

ACLs can be applied to router interfaces in either direction:

• Inbound ACLs: These are applied to traffic coming into an interface. The router processes the ACLs before routing the packet to the outbound interface².

• Outbound ACLs: These are applied to traffic leaving an interface. The router routes the packet first and then processes the ACLs at the outbound interface².