What protocol synchronizes with a private master clock or with a publicly available server on the internet?

The protocol that synchronizes with a private master clock or with a publicly available server on the internet is NTP (Network Time Protocol).

Here is an explanation of all the options provided:

1. TFTP (Trivial File Transfer Protocol): This is a simple, lockstep, file transfer protocol that is used to transfer files typically within a local network. It’s not used for synchronization purposes.
2. NTP (Network Time Protocol): This protocol is used to synchronize the clocks of computers to a reference time source, such as a master clock or an internet time server.
3. MPLS (Multiprotocol Label Switching): MPLS is a data-carrying technique for high-performance telecommunications networks. It does not deal with time synchronization but rather with directing data from one network node to the next based on short path labels rather than long network addresses.
4. CBWFQ (Class-Based Weighted Fair Queueing): This is a queueing mechanism used in network quality of service (QoS) that provides bandwidth allocation to specific classes of traffic. It does not provide time synchronization services.

So, for time synchronization with a master clock or public time servers, NTP is the correct protocol.