123
ntp
UDP · 0x007B
Port 123 — ntp
Others
Port 123 carries Network Time Protocol over UDP. Being at or below 1023, only root may open it on Unix.
0–1023. On Unix only root may open one.
Where it sits in 65535
A port number is 16 bits, so it stops at 65535. The narrow band at the left is everything up to 1023.
065535
- Service
- Network Time Protocol (ntp)
- Kind
- Others
- Protocol
- UDP
- Range
- Well-known
- Root needed
- Yes
- Hexadecimal
- 0x007B
- Binary
- 0000000001111011
- Two bytes
- 0 · 123
Same kind
Time, printing, play — the ones that fit nowhere else.
Ports next to it
How to read this
- A port number is 16 bits, so it runs 0 to 65535. There is no port 65536.
- Opening anything at or below 1023 needs root on Unix.
- Plain and encrypted often live on different numbers — 80 and 443, for one.
- Numbers like 3000 and 8080 were never registered; those are marked as custom.
Frequently asked questions
Q. What is port 123 used for?
Network Time Protocol (ntp) uses it, over UDP.
Q. Does opening port 123 need root?
Yes. It is at or below 1023, so on Unix only root may open it.
Q. Which range does port 123 fall in?
Well-known (0–1023). In hex it is 0x007B.
Q. Does port 123 have a twin?
Not a separate one. It either was encrypted from the start or negotiates TLS on the same number.