The use of access control lists (ACLs) is the MOST effective method to mitigate security risk for routers because they: (Identify Correct answer and…

Access Control Lists (ACLs) are a fundamental security feature of routers. They function as a set of rules that dictate whether to permit or deny traffic packets based on criteria such as source/destination IP addresses, port numbers, and protocols. Their primary effectiveness in mitigating risk comes from this specific filtering capability. By configuring ACLs, an administrator can explicitly block traffic from untrusted sources like the open Internet and prevent unauthorized access to sensitive router management protocols like Telnet, which transmits credentials in cleartext. This directly hardens the router and protects the internal network it serves.

A. are recommended by security standards.

While true, this states an endorsement rather than explaining the technical reason why ACLs are effective for risk mitigation.

C. act as filters between the world and the network.

This statement is too general. It describes a basic function of many network security devices, but option B provides the specific, critical actions that make ACLs effective on a router.

D. can detect cyberattacks.

This is functionally incorrect. ACLs are a preventative control that filters traffic based on predefined rules; they do not possess the analytical or signature-based capabilities to detect attacks like an Intrusion Detection System (IDS).

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1. ISACA

CISA Review Manual

27th Edition (2019). Domain 4: Information Systems Operations and Business Resilience

Section 4.4.2 Network Devices. The manual explains that routers use ACLs to filter packets based on rules

which can specify source/destination addresses and port numbers. This mechanism is used to enforce security policies by controlling traffic flow between networks

which is the basis for limiting traffic from the internet and protecting services like Telnet.

2. ISACA

CISA Glossary of Terms. The official glossary defines an Access Control List (ACL) as "A list of users and their permitted access rights to a resource." In the context of network routers

the "resource" is network traffic

and the "rights" are the permit/deny rules that form the basis of packet filtering. This definition supports the function described in the correct answer.

3. Kurose

J. F.

& Ross

K. W. (2017). Computer Networking: A Top-Down Approach (7th ed.). Pearson. Chapter 8

Security in Computer Networks

Section 8.6.2 Firewalls. University-level texts like this one detail how ACLs on routers form the basis of packet-filtering firewalls

explicitly used to block traffic based on IP addresses and TCP/UDP port numbers (e.g.

blocking Telnet port 23 from external addresses).