Ntp4 extension fields

Hello there. I’m fetching ntp time from a client using the us.pool.

I’m looking to use NTP v4 for use of the extension fields and higher precision for fetched time. However, I’m an unsure what field type to specificy in the extension format packet to request this.

Essentially, how can I find out about the supported field types from an ntp server in this pool; is there any documentation?

Is there a specification of the extension field or are you implementing your own? There is a range of values (0xF000-0xFFFF) specified for experimental use in this draft:

The pool servers run different NTP implementations. Only some of them can respond with an extension field. The only way to find out whether a server supports a specific extension field is to send a request with it and see if there is a response and what it contains.