Why do some protocols use the same port (say 53 of DNS) for both data inflow and outflow, while some protocols use different ports (say 21/20 for an FTP server) for inflow/outflow? -
Understanding How FTP Works
TCP port 21 FTP vulnerabilities - Specops Software
Beckhoff Information System - English
![What is FTP Port Number? [Default FTP Port]](https://monovm.com/wp-content/uploads/2022/04/what-is-ftp-port577-main.webp "What is FTP Port Number? [Default FTP Port]")
What is FTP Port Number? [Default FTP Port]
FTP Port: File Transfer and Port Numbers | ExaVault Blog
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Active vs. Passive FTP Simplified: Understanding FTP Ports | JSCAPE
Understanding the FTP PORT command | TechTarget
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How to setup port forwarding behind ADSL(Cable) router or firewall manually?
FTP control and Data connections. FTP uses control connection to… | by Ananthakrishnan | Medium
Port Number: The Significance of Port Numbers in FTP Connections - FasterCapital
Understanding FTP Ports: File Transfer & Port Numbers - YouTube
FTP Port: File Transfer and Port Numbers | ExaVault Blog
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TCP Port Number 21 and How It Works With FTP
21/tcp FTP – Enumeration | VK9 Security
Open ftp port 21 on windows XP operating system - nixCraft
Which ports should be opened for FTP access? - Microsoft Q&A
File Transfer Protocol - FTP
The TCP/IP Guide - FTP Data Connection Management, Normal (Active) and Passive Data Connections and Port Usage
FTP Ports | What is FTP? | FTP Modes | FTP Commands ⋆ IpCisco
Is Port 21 Secure? Fully Explained | ExaVault Blog
CompleteFTP: How to set a PASV port range
How to Change FTP Port in Linux? - GeeksforGeeks
What is port 21 and 20 for FTP? - Quora
