Hey Nadav,
I hope you are doing great,
So NTPv4 retains backwards compatibility with the older versions of NTP, including NTPv3 and NTPv2 but excluding NTPv1, which has been discontinued due to security vulnerabilities. So NTPv2/v3 are the official supported as the feature itself, but it can work with NTPv4 servers.
https://www.cisco.com/c/en/us/td/docs/switches/datacenter/nexus9000/sw/6-x/fundamentals/configuration/guide/b_Cisco_Nexus_9000_Series_NX-OS_Fundamentals_Configuration_Guide/b_Cisco_Nexus_9000_Series_NX-OS_Fundamentals_Configuration_Guide_chapter_01.h...
If you check the above link shows that for NX-OS the supported NTP standard as per IEEEE, now the way it is behaving, is to have backwards compatibility.
NTP has undergone a number of changes since its debut more than 30 years ago. NTP version 0 was defined in RFC 958 in September of 1985. NTPv0 was able to achieve time accuracy in the tens of milliseconds. In 1988, RFC 1059 defined NTPv1, which defined tuning of NTP for client server and peer to peer mode. In 1989, RFC 1119 defined NTPv2, which added things like a management protocol and an authentication scheme, which are still used in today’s version. RFC 1305, which came out in 1992, defined NTPv3. NTPv3 added additional error detection and analysis, which helps the client to choose between different tie sources. A broadcast mode was also introduced to help ease the distribution of time on a multi-access network. In 2010, RFC 5905 was published with the specifications for NTPv4 but was enhanced by RFC 7822 in March of 2016. NTPv4 is the current version of NTP. It maintains a lot of the same features of NTPv3 but adds support for IPv6 as the underlying network protocol. Authentication is also enhanced and gives the protocol greater security.
Really NTPv2 and V3 are pretty much the same only that V3 has other features, below some explanation on it:
In 1989, RFC 1119 was published defining NTPv2 by means of a state machine, with pseudocode to describe its operation. It introduced a management protocol and cryptographic authentication scheme which have both survived into NTPv4, along with the bulk of the algorithm. However the design of NTPv2 was criticized for lacking formal correctness by the DTSS community, and the clock selection procedure was modified to incorporate Marzullo's algorithm for NTPv3 onwards.
In 1992, RFC 1305 defined NTPv3. The RFC included an analysis of all sources of error, from the reference clock down to the final client, which enabled the calculation of a metric that helps choose the best server where several candidates appear to disagree. Broadcast mode was introduced.
Keep us posted if you have any question, please rate all helpful answers and select this as validated answer if I answered your question,
David Castro,
