NTP versions 3 and 4

Network Time Protocol (NTP) has several versions. NTPv4 has some improvements over NTPv3, one of which states that NTPv4 supports the IPv6 address family. This statement can be misleading, since NTPv3 can be encapsulated in an IPv6 packet.

The phrase “supports the IPv6 address family” simply means that some mechanisms and fields in the NTP header have been modified to take into account the use of IPv6 addresses, but this only refers to background processes such as MD5 hash generation, and the use of site-local multicast for IPv6, for example. RFC 5905 details these improvements including those pertaining to IPv6.

Ultimately, when configuring NTPv4, you won’t see any particular change in the configuration of the commands compared to NTPv3, especially because of the fact that NTPv4 is backward compatible with NTPv3.