21
FTP Control
File Transfer Protocol (control)
TCP
File Transfer
Port Information
Port Number
21
Protocol
TCP
Category
File Transfer
Common Usage
URL with Port
http://localhost:21 https://example.com:21
Node.js/Express Server
const express = require('express');
const app = express();
const PORT = 21;
app.listen(PORT, () => {
console.log(`Server running on port ${PORT}`);
});Docker Port Mapping
docker run -p 21:21 myapp # In docker-compose.yml ports: - "21:21"
Firewall Configuration
# Linux/Ubuntu firewall sudo ufw allow 21/tcp # Check if port is in use netstat -an | grep 21
Port 21 - FTP Control
File Transfer Protocol (control) This is a TCP port commonly used in file transfer applications. Port numbers range from 0-65535, with ports 0-1023 being well-known system ports, 1024-49151 being registered ports, and 49152-65535 being dynamic/private ports.