Proftpd doesn't answer to "PASV" command

I've been trying to configure my FTPS server which is behind NAT. so I've opened ports 20, 21 as well as 2120-2180 in my NAT (TCP+UDP) and configured proftpd to use this ports for passive communications. However, trying to connect using FileZilla leads to the following log: (in french, but quite clear actually) Statut : Résolution de l'adresse de heardrones.com Statut : Connexion à 93.30.208.56:21... Statut : Connexion établie, attente du message d'accueil... Réponse : 220 ProFTPD 1.3.5 Server (HEAR Server) [93.30.208.56] Commande : USER hear_downloader Réponse : 331 Mot de passe requis pour hear_downloader Commande : PASS ******** Réponse : 230 Utilisateur hear_downloader authentifié Commande : OPTS UTF8 ON Réponse : 200 UTF-8 activé Statut : Connecté Statut : Récupération du contenu du dossier... Commande : PWD Réponse : 257 "/" est le répertoire courant Commande : TYPE I Réponse : 200 Type paramétré à I Commande : PASV Erreur : Délai d'attente expiré Erreur : Impossible de récupérer le contenu du dossier It times out before even being capable of sending the "PASV" answer ! What could cause this ? The answer to PASV command uses the same port as all other commands (PWD, TYPE ...), so where could it come from ? ------------------------------- Here is the network design : Server Proftpd, no iptables, fix IP 192.168.0.13 -> (Wifi) ISP Box - French ISP (SFR) port transfer 20,21,22,2120-2180 to 192.168.0.13 -> (optic fiber !) Internet I can give Box settings screenshots and proftpd config files if needed. Connecting from LAN/Localhost works perfectly.