Port21— FTP
FTP utilise TCP 21 pour sa connexion de contrôle. Les fichiers passent par une connexion distincte ; une connexion réussie au compte ne garantit donc pas le bon fonctionnement des transferts.
Registry assignments, software defaults and local listeners are different things. A port number alone does not identify or secure a service.
Configuration and troubleshooting
Vérifiez le mode actif ou passif, la plage de ports de données configurée et les correspondances NAT. Ouvrir uniquement le port 21 ne suffit pas aux transferts passifs.
Important limitations
FTP seul ne chiffre pas les échanges. FTPS et SFTP basé sur SSH sont des protocoles différents, pas de simples réglages de port interchangeables.
Read-only checks: run on the server host
Choose the commands for your OS. Check TCP and UDP separately. No result is not a lasting availability guarantee; inspect host and container separately.
Linux
sudo ss -ltnp 'sport = :21'macOS
sudo lsof -nP -iTCP:21 -sTCP:LISTENWindows PowerShell
Get-NetTCPConnection -LocalPort 21 -State ListenSources and review
Sources checked on:
This review covers the explanations and sources on this page, not your device or every community software entry below.
Logiciels utilisant ce port (2 logiciels)
Community software entries: links are references, not individual verification.
Conseils d’utilisation
- Avant d’utiliser le port 21, vérifiez qu’il n’est pas occupé par d’autres services
- En cas de conflit de ports, envisagez d’utiliser d’autres ports ou d’arrêter le service qui occupe le port
Questions fréquentes
What is port 21 used for?
Port 21 sits in the File Sharing category. This page lists the registered purpose and the software commonly associated with it; to see what is actually listening on a specific machine, check the process with ss/netstat.
Is port 21 TCP or UDP?
The registered protocol on this page is TCP. The same number behaves independently on each protocol: TCP may be listening while UDP is idle, so check them separately.
How do I check if port 21 is in use?
On Linux: sudo ss -tlnp 'sport = :21' for an exact port match. On macOS: sudo lsof -nP -iTCP:21 -sTCP:LISTEN. On Windows PowerShell: Get-NetTCPConnection -LocalPort 21 -State Listen. A listener counts as confirmed only when you can see the bind address and process name; without root/admin you will not see other users' processes.
Is port 21 secure? Should I open it in my firewall?
A port number has no inherent security — it depends on whether the listening service is correctly configured and whether it needs exposure at all. Keep loopback/internal-only services firewalled; where public access is required, pair it with source restrictions, VPN or authentication. The caution section on this page lists port-specific risks.
En bref
- Port
- 21
- Protocole
- TCP
- Catégories
- Partage de fichiers
- État d’utilisation
- 2 logiciels utilisant ce port
Ports associés
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