An Application Layer utility transmits network administration and control messages between nodes. Which service should it use?

The correct response involves understanding the role of various protocols operating at the Application Layer and their services. An Application Layer utility that transmits network administration and control messages is best served by employing ICMP (Internet Control Message Protocol).

ICMP is a network layer protocol used primarily for diagnostics and error messaging. It helps in sending control messages such as destination unreachable, time exceeded, echo requests and replies (used in ping utilities), and other network communication tools. This makes ICMP ideal for tasks that require network management and control, as it is specifically designed for these purposes rather than for transmitting general application data.

In contrast, while TCP is connection-oriented and guarantees delivery of messages, it is designed for transferring larger amounts of application data reliably at higher layers. UDP, on the other hand, is connectionless and used for scenarios where speed is more critical than reliability, such as streaming media or real-time communications. ARP (Address Resolution Protocol) operates at a lower layer, mainly handling the mapping of IP addresses to MAC addresses on local area networks, which does not fit the context of network administration messages.

Therefore, the protocol tailored for transmitting control and administrative messages within the context of networking tools is ICMP.