What are ACLs?
ACLs are a set of instructions that are used to regulate access to network resources. Configured on network devices such as routers and switches, ACLs determine which traffic is allowed or denied in a network segment based on the following criteria:
- IP addresses
- Source IP address, which identifies the originating address of the traffic
- Destination IP address, which specifies the target address
- Protocol type
- The type of protocol (for example, TCP, UDP, ICMP).
- Port numbers
- The specific port numbers involved in the communication
- Traffic flow
- Direction of traffic (ingress or egress)
Operating as a fundamental security tool, ACLs help protect the network from external threats and limit potential attack vectors.
Note
ACLs primarily operate at Layer 3 (the network layer) and Layer 4 (the transport layer) of the OSI model.
Let’s look at an example:
Figure 7.22 – ACL example
In this example, we have several...
