Documentation forServ-U MFT & Serv-U FTP Server

Serv-U domain details: Listeners

The Domain Details: Listeners tab shows whether the listener is enabled, the IP address(es), port, and file sharing protocol.

Listeners defines how a domain accepts incoming connections. A domain can listen on multiple ports and IP addresses by adding listeners bound to the IP addresses and ports 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 for each.

The following file sharing protocols are supported by the Serv-U File Server:

Protocol Description Default Port

FTP and explicit SSL/TLS

FTP is the traditional protocol for transferring files over the Internet. Traditionally, FTP is handled in plain-text. However, SSL/TLS connections are explicitly supported through the use of the AUTH command.


Implicit FTPS (SSL/TLS)

FTPS is identical to FTP, although connecting to a listener configured for FTPS means an SSL/TLS connection is required before any protocol communication is performed. This is commonly referred to as Implicit FTPS.



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.



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.


HTTPS (SSL encrypted HTTP)

HTTPS is identical to HTTP except all communications are secured using the SSL/TLS protocol. Like FTPS, a secure connection is implied when connecting to a listener running the HTTPS protocol.


Add a listener

  1. Click Add.

    The Listener window is displayed.

  2. Select the protocol type (see the table above).
  3. The subsequent fields displayed depend on the protocol selected.

    IP Address

    Bind a listener to a single IP address by entering the IP address here. Serv-U supports both IPv4 and IPv6 addresses. 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 running a purely IPv6 network, it is recommended to use IPv4 addresses and add IPv6 listeners as needed.

    If the file server does not have an external IP address (for example, it is behind a router), you can leave this field blank.

    Port 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 using a non-standard port, it is recommended you use a value above 1024 to prevent potential conflicts.
    PASV IP Address or Domain Name

    If the listener supports the FTP or FTPS protocol, you can specify a separate IP address here to use for PASV (passive) mode data transfers. This ensures 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 here. 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 necessary to provide the PASV IP address to connecting clients. When 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.

Pure virtual domains

Serv-U allows multiple domains to "share" the same listeners. This means one domain can possess the necessary listener configurations while another domain "piggybacks" on it. 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 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.