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Domain listeners

Created by Anthony.Rinaldi_ret, last modified by Anthony.Rinaldi_ret on Jul 20, 2016

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The Serv-U File Server offers a highly configurable interface for enabling the different file sharing protocols on a domain. You can add, edit, and delete listeners. Each domain can listen on multiple ports and IP addresses by adding a listener bound to the IP address and port you want. In addition to selecting these connection attributes for a listener, you must also select a file sharing protocol. Serv-U supports IPv4 and IPv6 simultaneously. To offer services to both IPv4 and IPv6 users, create a listener both for an IPv4 address and an IPv6 address.

The following section contains the list and short description of the file sharing protocols supported by the Serv-U File Server.

FTP - File Transfer Protocol

FTP is the traditional protocol for transferring files over the Internet. It normally operates on the default port 21. Traditionally, FTP is handled in plain-text, however, SSL connections are explicitly supported through the use of the AUTH command.

FTPS - File Transfer Protocol using SSL

FTPS is identical to FTP, however, connecting to a listener configured for FTPS means that an SSL connection is required before any protocol communication is performed. This is commonly referred to as Implicit FTPS, which normally takes place on the default port 990.

SFTP - Secure File Transfer Using SSH2

SFTP is a secure method of transferring files through a secure shell session. It performs all protocol communications and data transfers over the same port eliminating the need to open multiple ports in firewalls as is commonly required when using FTP. SFTP sessions are always encrypted. SFTP operates on the default port 22.

HTTP - Hypertext Transfer Protocol

HTTP is the protocol used to browse websites. It is also a simple method for downloading and transferring files. One benefit to adding an HTTP listener to a domain is the availability of the Web Client, which allows users to transfer files to and from your file server without the need for a standalone client. HTTP traditionally operates on port 80.

HTTPS - Hypertext Transfer Protocol using SSL

HTTPS is identical to HTTP except all communications are secured using SSL. Like FTPS, a secure connection is implied when connecting to a listener running the HTTPS protocol. The default port for HTTPS is 443.

Add a listener

After clicking Add, the listener configuration window is displayed. After configuring each of the listener options, click Save to add the listener to the domain.

The following section contains the list and short description of the options you can configure for a listener.


Select the file sharing protocol that is to be supported by this listener. Each listener can only support a single protocol. To add more file sharing protocols to the domain, create new listeners for each protocol. A brief description of the supported file sharing protocols is found in the previous section.

IP Address

You can bound a listener to a single IP address by entering the IP address here. Serv-U supports both IPv4 and IPv6 addresses. If the file server does not have an external IP address (for example, it is behind a router), you can leave this field blank. If you do not specify an IP address, you must select the option to either listen on all available IPv4 addresses or all IPv6 addresses. Unless you are running a purely IPv6 network, it is recommended to use IPv4 addresses and add IPv6 listeners as needed.

PASV IP Address or Domain Name (FTP ONLY)

If the listener supports the FTP protocol, this additional field is available where you can specify a separate IP address to use for PASV mode data transfers. Entering an IP address here ensures that PASV mode works properly on both unsecured and secured connections. If the file server does not have an external IP address, try using a dynamic DNS service and entering your DNS domain name in this field. Serv-U resolves the DNS domain name to ensure it always has the proper external IP address for PASV command responses.

Use only with SSL connections

This option allows the PASV IP address or domain name to only be used for SSL connections where it is always necessary to provide the PASV IP address to connecting clients. When this option is enabled, the IP address specified for PASV mode will not be provided to clients connecting through non-SSL FTP.

Use with LAN connections

Normally, Serv-U does not use the PASV IP address for connections coming from the local area network (computers on the same network as Serv-U). When this option is enabled, the PASV IP Address is also used for LAN connections.


The default port for the selected protocol is automatically provided. However, you can use any port between 1 and 65535. When using a non-standard port, clients must know the proper port in advance when they attempt to connect to the domain. If you use a non-standard port, it is recommended that you use a value above 1024 to prevent potential conflicts.

Enable listener

You can temporarily disable a listener by deselecting this option. When they are disabled, listeners are displayed with a different icon in the list.

Pure virtual domains

Serv-U supports the ability for multiple domains to "share" the same listeners. In other words, one domain can possess the necessary listener configurations while the other domain "piggybacks" on the first one. In this way, the second domain exists in a virtual way. To have a domain "piggyback" on the listener configurations of existing domains, leave the listener list blank for the domain. The "piggybacking" domain needs to have at least one virtual host defined for it. For more information, see Virtual hosts.

This method of "piggybacking" only works with the FTP and HTTP protocols because they are the only two file sharing protocols that specify a method for identifying the specific host after a connection is established. For FTP connections, the client must issue a HOST command to identify the specific domain. For HTTP connections, the browser automatically handles providing the necessary host header to Serv-U based on the domain name that is used to establish the HTTP connection.

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