Cisco Certified Network Associate (CCNA) Practice Exam

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What command is used to permit or deny ICMP traffic in an extended ACL?

access-list ACL NUMBER permit/deny icmp SOURCE IP ADDRESS
access-list ACL NUMBER permit/deny ip SOURCE IP ADDRESS
ip nat source static PRIVATE IP ADDRESS
ip nat inside source list ACCESS LIST NUMBER

The correct answer is: access-list ACL NUMBER permit/deny icmp SOURCE IP ADDRESS

The command that is used to permit or deny ICMP traffic in an extended Access Control List (ACL) is correctly identified. Extended ACLs allow you to filter IP traffic based on various criteria, including the type of protocol and source/destination IP addresses. In this case, using "access-list ACL NUMBER permit/deny icmp SOURCE IP ADDRESS" directly specifies the ICMP protocol along with the source IP address, enabling you to control ICMP traffic specifically. This granularity is crucial for managing and securing networks, as ICMP is commonly used for functions like pinging and network troubleshooting but can also be abused for malicious purposes. The other options involve commands related to different functionalities. For instance, the command involving "ip nat" pertains to Network Address Translation and would not serve to filter ICMP traffic in an ACL context, as it deals more with how IP packets are translated between private and public addresses. Thus, focusing on ICMP in the intended command makes it the correct approach for controlling this type of traffic with an extended ACL.