Which statement best describes the difference between standard and extended ACLs in Cisco IOS?

Which statement best describes the difference between standard and extended ACLs in Cisco IOS?

• A. Standard ACLs filter by source IP only.
• B. Extended ACLs filter by source IP only.
• C. Standard ACLs filter by protocol and port.
• D. Extended ACLs filter by destination IP only.

Answer: (A)

ACLs in Cisco IOS determine whether to permit or deny traffic by inspecting fields of the packet. Standard ACLs examine only the source IP address, meaning they permit or deny traffic based on where it’s coming from, regardless of where it’s going or what service is being used. Extended ACLs, on the other hand, go further: they can filter by protocol (such as TCP, UDP, ICMP), and they can use both source and destination IP addresses plus port numbers to finely control specific services between specific hosts. That’s why the statement that standard ACLs filter by source IP only is the best description. The other options mix in capabilities that extended ACLs provide (like protocol and port filtering, or focusing on destination IP), which standard ACLs do not.

ACLs in Cisco IOS determine whether to permit or deny traffic by inspecting fields of the packet. Standard ACLs examine only the source IP address, meaning they permit or deny traffic based on where it’s coming from, regardless of where it’s going or what service is being used. Extended ACLs, on the other hand, go further: they can filter by protocol (such as TCP, UDP, ICMP), and they can use both source and destination IP addresses plus port numbers to finely control specific services between specific hosts.

That’s why the statement that standard ACLs filter by source IP only is the best description. The other options mix in capabilities that extended ACLs provide (like protocol and port filtering, or focusing on destination IP), which standard ACLs do not.