Cisco Certified Internetwork Expert (CCIE) Practice Test

Which two options are standard functionalities of ICMP?

1. Packet filtering

2. Host detection

3. Relaying traffic statistics to applications

4. Path MTU discovery

The correct answer is: Host detection

The correct choice highlights one of the critical functionalities of ICMP (Internet Control Message Protocol), which is host detection. ICMP is widely used for network diagnostics and operations, with one of its main roles being to facilitate the detection of network hosts. This can be achieved through various ICMP message types, such as Echo Request and Echo Reply, which are used in tools like "ping." When a device sends an Echo Request to a specific IP address, it awaits an Echo Reply from the host at that address, effectively confirming whether the host is reachable and active on the network. In contrast, packet filtering pertains to security measures that control the data packets allowed to enter or leave a network, which is not a function of ICMP. Relaying traffic statistics to applications is also outside the standard functionalities of ICMP, as ICMP primarily focuses on network message transmission for troubleshooting and status reports, rather than extensive statistics gathering and reporting for applications. Path MTU discovery is a process used to determine the maximum transmission unit size on the path between two IP hosts, which also utilizes ICMP messages, but it does not specifically relate to host detection as indicated in the correct choice.