How to Enable FTP Passive Mode

Overview

This document explains how to use the active or passive mode to connect to a File Transfer Protocol (FTP) server.

Active and passive mode sessions

FTP uses a data port and a command port to transfer information between a client and a server. During a typical active mode session, the command port uses port 21 and the data port uses port 20. When you use a passive mode session, however, the data port does not always use port 20.

Active

In active mode, the FTP server responds to the connection attempt and returns a connection request from a different port to the FTP client. Network Address Translation (NAT) configurations block this connection request.

The firewall blocks the server’s attempt to communicate with the client because the server uses a different port than the first connection.

Passive

In passive mode, the FTP client initiates both connection attempts. NAT configurations do not block this connection request.

The firewall does not block the server’s attempt to communicate with the client because the client initiated the communication both times.

Configure FTP servers

The sections below explain how to edit the default configurations for a Pure-FTPd server and a ProFTPD server.

Pure-FTPd servers

To edit the FTP configuration for a PureFTP server, perform the following steps:

1. Log in to the server as the root user via SSH.
2. Open the /var/cpanel/conf/pureftpd/local file, if it already exists, with a text editor. If it does not already exist, create the /var/cpanel/conf/pureftpd/local file.
3. Add the desired changes to the file. If your FTP server exists behind a NAT configuration, set the ForcePassiveIP option to the FTP server’s public IP address, as in the following example:

   ForcePassiveIP: 203.0.113.0

   If your server does not exist in a NAT configuration, set the ForcePassiveIP option to the following entry:

   ForcePassiveIP: ~

   Important:

   Only one ForcePassiveIP entry can exist in a configuration file.
4. If you want to change your server’s default passive port range, run the following commands:

   1 2	echo "PassivePortRange: 49152 65534" >> /var/cpanel/conf/pureftpd/local /usr/local/cpanel/scripts/setupftpserver pure-ftpd --force

5. Configure your server to allow the passive port range to pass through the firewall. To do this, follow the directions in the Configure the firewall section below.
6. Restart the PureFTP service with the following command:

   /usr/local/cpanel/scripts/setupftpserver pure-ftpd --force

ProFTPD servers

To edit the FTP configuration for a ProFTPD server, perform the following steps:

1. Log in to the server as the root user via SSH.
2. Open the /var/cpanel/conf/proftpd/local file, if it already exists, with a text editor. If it does not already exist, create the /var/cpanel/conf/proftpd/local file.
3. Add the desired changes to the file. If your FTP server exists behind a NAT configuration, set the MasqueradeAddress option to the FTP server’s public IP address, as in the following example:

   MasqueradeAddress: 203.0.113.0

   If your server does not exist in a NAT configuration, set the MasqueradeAddress option to the following entry:

   MasqueradeAddress: ~

   Important:

   Only one MasqueradeAddress entry can exist in a configuration file.
4. If you want to change your server’s default passive port range, run the following commands:

   1 2	echo "PassivePorts: 49152 65534" >> /var/cpanel/conf/proftpd/local /usr/local/cpanel/scripts/setupftpserver proftpd --force

5. Configure your server to allow the passive port range to pass through the firewall. To do this, follow the directions in the Configure the firewall section below.
6. Restart the ProFTP service with the following command:

   /usr/local/cpanel/scripts/setupftpserver proftpd --force

Configure the firewall

You may need to add your FTP server’s passive port range to the firewall manually.

ConfigServer Security & Firewall

If you use the ConfigServer Security & Firewall (CSF) plugin to manage your server’s firewall, open the /etc/csf/csf.conf file, and confirm that the passive port range exists at the end of the TCP_IN line. The system adds your FTP server’s passive port range to the firewall by default. For more information about how to install and use CSF, visit the CSF website.

nftables

If you use the nftables framework for your CentOS 8, AlmaLinux 8, or CloudLinux 8 server, run the following commands to add the passive port range to your server’s firewall:

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nft add rule filter INPUT tcp dport 49152-65534 accept
nft -s list ruleset | tee /etc/sysconfig/nftables.conf # to save the ruleset post reboot

You will find the nftables ruleset for your server in the /etc/sysconfig/nftables.conf file.

firewalld

If you use the firewalld application for your CentOS 7, CloudLinux™ 7, or Red Hat® Enterprise Linux (RHEL) 7 server, run the following commands to add the passive port range to your server’s firewall:

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firewall-cmd --permanent --zone=public --add-service=ftp
firewall-cmd --permanent --add-port=49152-65534/tcp
firewall-cmd --reload

iptables

If you use the iptables application for your FTP server’s firewall, perform the following steps to add the passive port range to your server’s firewall:

1. Install the iptables-services package if it does not already exist on your server. This package provides the iptables and ip6tables services, which are not included in the iptables application. To install this package, run the following command:

   yum install iptables-services

2. Run the following commands to add the rules to the firewall and save the configuration:

   1 2	iptables -I INPUT -p tcp --dport 49152:65534 -j ACCEPT service iptables save

SolusVM and Xen

If you use SolusVM and Xen® on a CloudLinux™ server, you may experience problems with Passive FTP. These problems may resemble a firewall or other connection issue, even when no firewall exists.

To resolve these issues, perform the following steps:

1. Replace the IPTABLES_MODULES= ip_conntrack_netbios_ns line in the /etc/sysconfig/iptables-config file on the VPS node with the following line:

   IPTABLES_MODULES=ipt_REJECT ipt_tos ipt_TOS ipt_LOG ip_conntrack ipt_limit ipt_multiport iptable_filter iptable_mangle ipt_TCPMSS ipt_tcpmss ipt_ttl ipt_length ipt_state iptable_nat ip_nat_ftp ipt_owner ipt_REDIRECT

2. Run the service iptables restart command to restart the iptables service.

Troubleshoot FTP passive mode

If your NAT-configured server cannot execute Passive FTP connections to other IP addresses on the server, perform either of the following actions:

• In cPanel & WHM version 66 and later, set the ForcePassiveIP option with a tilde (~) character. The system interprets this character as an undefined directive and prevents automatic changes to the /etc/pure-ftpd.conf or /etc/proftpd.conf files.
• In cPanel & WHM version 64 and earlier, follow the directions in our Passive FTP and NAT Configuration Temporary Workaround documentation.