Which statement correctly describes standard versus extended ACLs on a router?

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

Answer: (A)

Standard ACLs filter traffic using only the source IP address. That means they decide whether to permit or deny packets based on where the traffic originated, not on where it’s going, what protocol it uses, or what port numbers are involved.

Extended ACLs expand this by considering the protocol (like TCP, UDP, ICMP) and port numbers, and they also evaluate the destination IP address, allowing much more granular control over what traffic is allowed or denied.

So, the statement that standard ACLs filter traffic by source IP only is the best description. The other options either imply filtering by destination IP alone, by protocol and port (which standard ACLs don’t do), or describe extended ACLs in a way that omits their IP-based filtering as well.