IPv6 is supported by Rebex FTP client. At the moment Rebex FTP prefers IPv4 addresses and only uses IPv6 address if no IPv4 address is available for a hotname.
I prepared a code that tries to connect to the first IPv6 address available and it reports that there are actually no IPv6 addresses for the "ftp.ripe.net" FTP server.
IPHostEntry ipEntry = Dns.GetHostEntry("ftp.ripe.net");
IPAddress addresses = ipEntry.AddressList;
IPAddress ipv6 = null;
foreach (var address in addresses)
if (address.AddressFamily == System.Net.Sockets.AddressFamily.InterNetworkV6)
ipv6 = address;
if (ipv6 == null)
throw new ApplicationException("No IPv6 address");
Ftp ftp = new Ftp();
Running the code, are you sure there is an IPv6 address for your FTP server?