# Network Time Protocol MAC/Last Extension Fields

**URL:** <https://community.nwtime.org/t/network-time-protocol-mac-last-extension-fields/337>\
**Category:** Documentation\
**Created:** [February 12, 2026, 3:54pm UTC](https://community.nwtime.org/t/network-time-protocol-mac-last-extension-fields/337 "2026-02-12T15:54:00Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![Dru](https://sea1.discourse-cdn.com/flex001/user_avatar/community.nwtime.org/dru/32/337_2.png) [@Dru](https://community.nwtime.org/u/Dru)\
**Post date:** [February 12, 2026, 3:54pm UTC](https://community.nwtime.org/t/network-time-protocol-mac-last-extension-fields/337/1 "2026-02-12T15:54:00Z")

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> **[Network Time Protocol MAC/Last Extension Fields](https://www.ntp.org/documentation/ietf/ntp-mac-last-ef/)**
>
> NTP packets can be authenticated by a Message Authentication Code (MAC) if a MAC is present at the end of an NTP packet. The legacy format for this MAC is not formatted as an NTP Extension Field, and its presence may cause some implementations a...