Which protocol is designed to time-synchronize a network of machines?

The Network Time Protocol (NTP) is a networking protocol specifically engineered for synchronizing the clocks of computer systems over packet-switched, variable-latency data networks. Its primary function is to ensure that all participating devices on a network share a consistent and accurate time reference. This is critical for various network operations, including log file correlation for security and troubleshooting, transaction sequencing, and certificate validation. NTP operates using a hierarchical, client-server model with different "stratum" levels to denote the distance from an authoritative time source, thereby providing a robust and precise time synchronization service across the network.

B. Cisco Discovery Protocol: This is a Cisco-proprietary protocol used for discovering information about directly connected Cisco devices, not for time synchronization.
C. Domain Name System (DNS): This protocol's function is to translate human-readable domain names into machine-readable IP addresses, not to manage time.
D. Dynamic Host Configuration Protocol (DHCP): This protocol automates the assignment of IP addresses and other network configuration parameters; it does not perform time synchronization itself.

1. Cisco Systems, Inc. (2023). IP Addressing: DHCP and DNS Configuration Guide, Cisco IOS XE Gibraltar 16.12.x. Chapter: System Management, Section: Configuring NTP. "The Network Time Protocol (NTP) is a protocol designed to time-synchronize a network of machines."

2. Mills, D. (June 2010). RFC 5905: Network Time Protocol Version 4: Protocol and Algorithms Specification. Internet Engineering Task Force (IETF). Abstract. "The Network Time Protocol (NTP) is widely used to synchronize computer clocks in the Internet."

3. Cisco Systems, Inc. (2023). Layer 2 Configuration Guide, Cisco IOS XE Bengaluru 17.6.x. Chapter: Configuring Cisco Discovery Protocol. This document describes CDP as a protocol for gathering information about neighboring Cisco devices, confirming it is not for time services.