Some FTP operations work and some do not – what can I do?

FTP failing to work is normally due to a firewall which is failing to allow through legitimate traffic. The FTP protocol is complicated and was designed in the 1970s, but was not designed with firewalls in mind. For very similar reasons, connections for which your Internet Service Provider uses a technology called “Carrier-grade NAT” will not work. Carrier-grade NAT is a way in which service providers who haven’t yet upgraded their networks to the modern IPv6 Internet protocol attempt to work around some of the limitations of the older IPv4 protocol and the problems of lack of available IPv4 addresses. Unfortunately, carrier-grade NAT is inherently (unfixably) incompatible with encrypted FTP connections. Carrier-grade NAT is most commonly seen on mobile telephone networks. If you are on a mobile network and FTP is not working for you, then this is almost certainly the cause.

If you have a personal firewall product on your computer, such as ZoneAlarm, you should turn it off and see if your problem continues. If this solves your problem, you should configure your firewall to add an exception for traffic coming from

You can also try the same operation from a different computer or network; if it works from there but not from your own computer then the problem is somewhere at your end and you should ask a technically knowledgeable person for help.

Alternatively you can use SFTP instead of FTP – your FTP program may have an option for this. SFTP is much more firewall-friendly than FTP. If you only have an Internet connection which uses carrier-grade NAT then this is your only option.

Posted in: Questions about FTP