[ntp:questions] NTP packets with MACs longer than SHA1

[Nelson Bolyard]

NTPv3 supported MD5 and SHA1 Message Authentication Code (MACs) of length 16 and 20 bytes respectively.  RFC 5906 says that NTP V4 supports any MAC, but offers no advice about how to send MACs that are longer than 20 bytes, such as SHA256 MACs.

Are longer MACs sent in their entirety?
Are they truncated to 20 bytes? or to 16 bytes?

Regards,