21
ftp
TCP · 0x0015
Port 21 — ftp
Files
Port 21 carries File Transfer Protocol over TCP. Being at or below 1023, only root may open it on Unix. Its encrypted twin is 990.
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
- File Transfer Protocol (ftp)
- Kind
- Files
- Protocol
- TCP
- Range
- Well-known
- Root needed
- Yes
- Hexadecimal
- 0x0015
- Binary
- 0000000000010101
- Two bytes
- 0 · 21
- Encrypted twin
- 990
Same kind
Moving files about, or sharing a disk.
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 21 used for?
File Transfer Protocol (ftp) uses it, over TCP.
Q. Does opening port 21 need root?
Yes. It is at or below 1023, so on Unix only root may open it.
Q. Which range does port 21 fall in?
Well-known (0–1023). In hex it is 0x0015.
Q. Is there an encrypted version of port 21?
Port 990 does the same thing wrapped in TLS.