Port 69: TFTP
Port 69 is TFTP, a very simple file transfer protocol with no login at all.
What runs on port 69
TFTP servers answer on UDP 69 and hand out or accept files to anyone who asks by name. It exists because it is tiny enough to fit in boot firmware, which is why it is used for network booting (PXE) and for loading configuration onto phones and network gear. There is no authentication or encryption.
On a home network
VoIP desk phones fetch configuration over TFTP, and some routers and switches use it for firmware recovery. A NAS or Pi can run a TFTP server for network booting. Typical home devices do not listen on 69.
If port 69 is reachable from the internet
A TFTP server on the internet lets anyone download any file they can guess the name of, which often includes device configurations containing passwords, and may let them upload files. It should never be exposed.
How to check whether it is open on your network
If you run a TFTP server on a NAS or Pi for booting or phone provisioning, make sure no router rule forwards UDP 69. An outside scan of your public address confirms it.
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