Which NTP type designates a router without an external reefrence clock as an authoritative time source?

A 'server' simply provides time, but it isn't inherently authoritative without an external reference unless specifically configured as a master.

A 'peer' exchanges time with other NTP servers for synchronization, but it does not designate itself as an authoritative time source without an external reference.

The 'master' NTP type, typically configured with the `ntp master` command, allows a router to act as an authoritative stratum 1 server, even if it is not synchronized to an external clock, making it a local source of time for other devices.

A 'client' requests time from an NTP server and synchronizes its clock to that server, it does not act as an authoritative time source.